#include "bits/stdc++.h"

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep1(i, n) for (int i = 1; i < (n); ++i)
#define rep1n(i, n) for (int i = 1; i <= (n); ++i)
#define repr(i, n) for (int i = (n) - 1; i >= 0; --i)
#define pb push_back
#define eb emplace_back
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define each(x, a) for (auto &x : a)
#define ar array
#define vec vector
#define range(i, n) rep(i, n)

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using str = string;
using pi = pair<int, int>;
using pl = pair<ll, ll>;

using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pair<int, int>>;
using vvi = vector<vi>;

int Bit(int mask, int b) { return (mask >> b) & 1; }

template<class T>
bool ckmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool ckmax(T &a, const T &b) {
    if (b > a) {
        a = b;
        return true;
    }
    return false;
}

const int INFi = 1e9;
const ll INF = 3e18;
const int LG = 18;

void solve() {
    int n, m; cin >> n >> m;
    vector<int> c(n);
    ll ans = 0;
    rep(i, n) {
        int a, b; cin >> a >> b;
        ans += a;
        c[i] = b - a;
    }
    if (n == 1) {
        cout << ans + c[0] << '\n';
        return;
    }
    sort(rall(c));
    ll cur = ans;
    rep(i, n - 2) {
        int total = (i + 1) * 2 + (n - 1 - i);
        cur += c[i];
        if (total <= m) ans = max(ans, cur);
    }
    if (n * 2 - 1 <= m) ans = max(ans, cur + c[n - 2] + c[n - 1]);
    cout << ans << '\n';
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(12) << fixed;
    int t = 1;
    cin >> t;
    rep(i, t) {
        solve();
    }
    return 0;
}