#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 5e5 + 1;
int n, m, K;
int a[N], b[N];
int c[N << 1];

struct segtree {
    struct node {
        ll x, y;
    }tree[(N * 2) << 2];

    ll tag[(N * 2) << 2];

    #define ls(cur) (cur << 1)
    #define rs(cur) (cur << 1 | 1)

    void addtag(int cur, ll k) {
        tree[cur].x += k;
        tree[cur].y += k;
        tag[cur] += k;
    }

    void pushdown(int cur) {
        if(!tag[cur]) return;
        addtag(ls(cur), tag[cur]);
        addtag(rs(cur), tag[cur]);
        tag[cur] = 0;
    }

    void build(int cur, int lt, int rt) {
        tag[cur] = 0;
        if(lt == rt) {
            tree[cur].x = -1ll * c[lt] * m;
            tree[cur].y = 0;
            return;
        }
        int mid = (lt + rt) >> 1;
        build(ls(cur), lt, mid);
        build(rs(cur), mid + 1, rt);
        tree[cur].x = max(tree[ls(cur)].x, tree[rs(cur)].x);
        tree[cur].y = max(tree[ls(cur)].y, tree[rs(cur)].y);
    }

    void update(int cur, int lt, int rt, int qx, int qy, int k) {
        if(lt > qy || rt < qx) return;
        if(lt >= qx && rt <= qy) {
            // cerr << lt << " " << rt << ": ";
            addtag(cur, k);
            // cerr << tree[cur].x << "\n";
            return;
        }
        pushdown(cur);
        int mid = (lt + rt) >> 1;
        update(ls(cur), lt, mid, qx, qy, k);
        update(rs(cur), mid + 1, rt, qx, qy, k);
        tree[cur].x = max(tree[ls(cur)].x, tree[rs(cur)].x);
        tree[cur].y = max(tree[ls(cur)].y, tree[rs(cur)].y);
    }

    node query(int cur, int lt, int rt, int qx, int qy) {
        if(lt > qy || rt < qx) return node{-(ll)1e18, -(ll)1e18};
        if(lt >= qx && rt <= qy)
            return tree[cur];
        pushdown(cur);
        int mid = (lt + rt) >> 1;
        node la = query(ls(cur), lt, mid, qx, qy), ra = query(rs(cur), mid + 1, rt, qx, qy);
        return node{max(la.x, ra.x), max(la.y, ra.y)};
    }
}T;

void solve() {
    cin >> n >> m;
    K = 0;
    c[++K] = 0;
    for(int i = 1; i <= n; ++i) {
        cin >> a[i] >> b[i];
        c[++K] = a[i];
        c[++K] = a[i] - 1;
    }
    sort(c + 1, c + K + 1);
    K = unique(c + 1, c + K + 1) - c - 1;
    T.build(1, 1, K);
    for(int i = 1; i <= n; ++i) {
        a[i] = lower_bound(c + 1, c + K + 1, a[i]) - c;
        ll ta = T.query(1, 1, K, 1, a[i] - 1).y - 1ll * c[a[i]] * m + b[i];
        ll tb = T.query(1, 1, K, a[i], K).x;
        // cerr << T.query(1, 1, K, K, K).x << " + " << b[i] << " = ";
        T.update(1, 1, K, a[i], K, b[i]);
        ll tmp = T.query(1, 1, K, a[i], a[i]).x;
        if(ta > tmp)
            T.update(1, 1, K, a[i], a[i], ta - tmp);

        tmp = T.query(1, 1, K, a[i] - 1, a[i] - 1).x;
        if(tb > tmp)
            T.update(1, 1, K, a[i] - 1, a[i] - 1, tb - tmp);

    }
    cout << T.query(1, 1, K, 1, K).x << "\n";
}

int main() {
    // freopen("1.in", "r", stdin);
    // freopen("1.out", "w", stdout);
    ios :: sync_with_stdio(false);
    int t;
    cin >> t;
    while(t--) solve();
    return 0;
}