#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ul unsigned ll
#define LL __int128_t
#define db double
#define DB long db
#define pii pair<int, int>
#define fi first
#define se second
#define mkpr make_pair
#define vi vector<int>
#define vl vector<ll>
#define vii vector<pii>
#define rsz resize
#define eb emplace_back
#define all(c) (c).begin(), (c).end()
#define bit(k) (1 << (k))
#define Bit(k) (1ll << (k))
#define BIT(k) ((LL)1 << (k))
#define lowbit(x) ((x) & -(x))
#define bin(s, k) ((s) >> (k) & 1)
#define lg2(x) (31 - __builtin_clz(x))
#define LG2(x) (63 - __builtin_clzll(x))
#define popcnt(x) __builtin_popcount(x)
#define mem(a, x) memset(a, x, sizeof(a))
#define req(i, l, r) for (int i(l), i##End(r); i < i##End; i = -~i)
#define rep(i, l, r) for (int i(l), i##End(r); i <= i##End; i = -~i)
#define per(i, r, l) for (int i(r), i##End(l); i >= i##End; i = ~-i)

// #define FILERR

#ifdef JYR
#ifdef FILERR
auto filerr = fopen("Test.err", "w");
#else
auto filerr = stderr;
#endif
#define errs(x) fputs(x "\n", filerr)
#define errm(x, ...) fprintf(filerr, x, ##__VA_ARGS__)
#else
#define errs(x) 0
#define errm(x, ...) 0
#endif

template<typename T, typename U> void chkmx(T &_a, U _b) { if (_a < _b) _a = _b; }
template<typename T, typename U> void chkmn(T &_a, U _b) { if (_b < _a) _a = _b; }

bool Mbe;

struct FastIO {
    char buf[1 << 20], *p1, *p2;
    char puf[1 << 20], *pf;

    FastIO() : p1(buf), p2(buf), pf(puf) {}
    ~FastIO() { fwrite(puf, 1, pf - puf, stdout); }

    char gc() {
        if (p1 == p2) p2 = (p1 = buf) + fread(buf, 1, 1 << 20, stdin);
        return p1 == p2 ? EOF : *p1++;
    }

    bool blank(char c) { return c == ' ' || c == '\r' || c == '\n' || c == '\t'; }

    char rd() {
        char c = gc(); while (blank(c)) c = gc();
        return c;
    }

    template<typename T> T rd() {
        T x = 0; int f = 0; char c = gc();
        while (!isdigit(c)) f = (c == '-'), c = gc();
        while (isdigit(c)) x = (x << 1) + (x << 3) + (c - '0'), c = gc();
        return f ? -x : x;
    }

    int rds(char *s) {
        char c = gc(), *S = s;
        while (blank(c)) c = gc();
        while (!blank(c) && c != EOF) *s++ = c, c = gc();
        return *s = 0, abs(s - S);
    }

    int rdl(char *s) {
        char c = gc(), *S = s;
        while (c == '\r' || c == '\n') c = gc();
        while (c != '\r' && c != '\n' && c != EOF) *s++ = c, c = gc();
        return *s = 0, abs(s - S);
    }

    void rd(char &c) { c = rd(); }

    void rd(char *s) {
        char c = gc();
        while (blank(c)) c = gc();
        if (c == EOF) { *s = 0; return; }
        while (!blank(c) && c != EOF) *s++ = c, c = gc();
        *s = 0;
    }

    template<typename T> void rd(T &x) {
        x = 0; int f = 0; char c = gc();
        while (!isdigit(c)) f = (c == '-'), c = gc();
        while (isdigit(c)) x = (x << 1) + (x << 3) + (c - '0'), c = gc();
        if (f) x = -x;
    }

    template<typename T, typename... Ts>
    void rd(T& x, Ts&... xs) { rd(x), rd(xs...); }

    void pc(const char &c) {
        if (pf - puf == 1 << 20) fwrite(pf = puf, 1, 1 << 20, stdout);
        *pf++ = c;
    }

    void prt(char c) { pc(c); }
    void prt(char* s) { while (*s) pc(*s++); }
    void prt(const char* s) { while (*s) pc(*s++); }

    template<typename T> void prt(T x) {
        static int st[41], tp = 0;
        if (x == 0) { pc('0'); return; }
        if (x < 0) x = -x, pc('-');
        while (x) st[++tp] = x % 10, x /= 10;
        while (tp) pc(st[tp--] + '0');
    }

    template<typename T> void prt(T *x) { while (*x) pc(*x++); }

    template<typename T, typename... Ts>
    void prt(T x, Ts... xs) { prt(x), prt(xs...); }

    void prts(const char *s, char c = '\n') {
        while (*s) pc(*s++);
        if (c) pc(c);
    }
} IO;

#define rd IO.rd
#define rdl IO.rdl
#define ri rd<int>()
#define rl rd<ll>()
#define prt IO.prt
#define prs IO.prts
#define edl IO.pc('\n')

#define MC

#define N 1000005
#define mod 998244353
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f

int n, m;
ll w;
int a[N];
ll b[N];
ll f[N], g[N], h[N];
vi _;

struct SegTree {
    #define lc (i << 1)
    #define rc (lc | 1)
    
    ll mx[N << 2], xm[N << 2], tg[N << 2];
    
    void psu(int i) { mx[i] = max(mx[lc], mx[rc]), xm[i] = max(xm[lc], xm[rc]); }
    void chg(int i, ll k) { mx[i] += k, xm[i] += k, tg[i] += k; }
    void psd(int i) { if (ll &k = tg[i]; k) chg(lc, k), chg(rc, k), k = 0; }
    
    void bld(int i = 1, int l = 0, int r = m) {
        if (l == r) { xm[i] = (mx[i] = !l ? 0 : -INF) + _[l] * w, tg[i] = 0; return; }
        int t = (l + r) >> 1;
        bld(lc, l, t), bld(rc, t + 1, r), psu(i);
    }
    
    void mdfA(int L, int R, ll k, int i = 1, int l = 0, int r = m) {
        // errm("mdfA(%d, %d, %lld, %d, %d, %d)\n", L, R, k, i, l, r);
        if (L <= l && r <= R) return chg(i, k);
        int t = (l + r) >> 1; psd(i);
        if (L <= t) mdfA(L, R, k, lc, l, t);
        if (t < R) mdfA(L, R, k, rc, t + 1, r);
        return psu(i);
    }
    
    void mdfX(int p, ll k, int i = 1, int l = 0, int r = m) {
        // errm("mdfX(%d, %lld, %d, %d, %d)\n", p, k, i, l, r);
        if (l == r) { chkmx(mx[i], k), chkmx(xm[i], k + _[l] * w); return; }
        int t = (l + r) >> 1; psd(i);
        return p <= t ? mdfX(p, k, lc, l, t) : mdfX(p, k, rc, t + 1, r);
    }
    
    ll qryX(int L, int R, int i = 1, int l = 0, int r = m) {
        // errm("qryX(%d, %d, %d, %d, %d)\n", L, R, i, l, r);
        if (L <= l && r <= R) return mx[i];
        int t = (l + r) >> 1; psd(i);
        ll res = -INF;
        if (L <= t) chkmx(res, qryX(L, R, lc, l, t));
        if (t < R) chkmx(res, qryX(L, R, rc, t + 1, r));
        return res;
    }
    
    ll qryM(int L, int R, int i = 1, int l = 0, int r = m) {
        // errm("qryM(%d, %d, %d, %d, %d)\n", L, R, i, l, r);
        if (L <= l && r <= R) return xm[i];
        int t = (l + r) >> 1; psd(i);
        ll res = -INF;
        if (L <= t) chkmx(res, qryM(L, R, lc, l, t));
        if (t < R) chkmx(res, qryM(L, R, rc, t + 1, r));
        return res;
    }
    
    // void dbg(int i = 1, int l = 0, int r = m) {
    //     errm("dbg(%d, %d, %d): %lld %lld %lld\n", i, l, r, mx[i], xm[i], tg[i]);
    //     if (l == r) return;
    //     int t = (l + r) >> 1;
    //     dbg(lc, l, t), dbg(rc, t + 1, r);
    // }
} T;

void mslv() {
    rd(n, w), _.rsz(1), _[0] = 0;
    rep(i, 1, n) rd(a[i], b[i]), _.eb(a[i]), b[i] < 0 && _.eb(a[i] - 1);
    sort(all(_)), _.rsz(unique(all(_)) - _.begin()), m = _.size() - 1;
    // errm("_:"); for (auto x : _) errm(" | %d", x); errs(" |");
    rep(i, 1, n) ;
    T.bld();
    // T.dbg();
    // f[0] = 0; rep(j, 1, m) f[j] = -INF;
    rep(i, 1, n) {
        // errm("---------- i = %d: [%d %lld] ----------\n", i, a[i], b[i]);
        int u = lower_bound(all(_), a[i]) - _.begin();
        if (b[i] >= 0) {
            ll x = T.qryM(0, u) - a[i] * w;
            // errm("x = %lld\n", x);
            T.mdfX(u, x), T.mdfA(u, m, b[i]);
            // rep(j, 0, m) g[j] = -INF;
            // rep(j, 0, m) h[j] = f[j] + _[j] * w;
            // rep(j, 1, m) chkmx(h[j], h[j - 1]);
            // per(j, m, 1) chkmx(f[j - 1], f[j]);
            // rep(j, 0, m) g[j] = max(h[j] - _[j] * w, f[j]);
            // rep(j, a[i], m) g[j] += b[i];
            // rep(j, 0, m) chkmx(ans, f[j] = g[j]);
        } else {
            int v = lower_bound(all(_), a[i] - 1) - _.begin();
            ll x = T.qryX(v + 1, m);
            ll y = T.qryM(0, u) - a[i] * w;
            // errm("x = %lld | y = %lld\n", x, y);
            T.mdfX(v, x), T.mdfX(u, y), T.mdfA(u, m, b[i]);
        }
        // T.dbg();
    }
    prt(T.qryX(0, m)), edl;
}

/*

设 f[i][j] 表示前 i 个人中第 i 个人被打了 j 次的最大收益。

f[i][j] <- f[i - 1][k] - max(j - k, 0) w + [j >= a[i]] b[i]

f[i][j] <- f[i - 1][k] + k w - j w + [j >= a[i]] b[i] (j >= k)
f[i][j] <- f[i - 1][k] + [j >= a[i]] b[i] (j < k)

*/

void mprw() {}

bool Med;

int main() {
    #ifdef JYR
    errs("Running!");
    freopen("Test.in", "r", stdin);
    freopen("Test.out", "w", stdout);
    #endif
    mprw();
    #ifdef MC
    int _ = ri;
    while (_--) mslv();
    #else
    mslv();
    #endif
    errm("%.3lfMB %.0lfms\n", abs(&Med - &Mbe) / 1048576., clock() * 1000. / CLOCKS_PER_SEC);
    return 0;
}