#include <bits/stdc++.h>

using namespace std;

const int N = 5e5 + 5;

int a[N];

signed main()
{
    int T;
    scanf("%d", &T);
    while (T--) {
        int n, m;
        scanf("%d%d", &n, &m);
        long long s = 0;
        for (int i = 1; i <= n; ++i) {
            int x, y;
            scanf("%d%d", &x, &y);
            s += y;
            a[i] = x - y;
        }
        if (n == 1) {
            printf("%lld\n", s);
            continue;
        }
        sort(a + 1, a + n + 1);
        reverse(a + 1, a + n + 1);
        int ct = max(n + n - m, 0);
        if (ct == 1) {
            ct = 0;
        }
        for (int i = 1; i <= ct; ++i) {
            s += a[i];
        }
        long long res = s;
        if (ct) {
            for (int i = ct + 1; i <= n; ++i) {
                s += max(a[i], 0);
            }
        } else {
            s += a[1] + a[2];
            for (int i = 3; i <= n; ++i) {
                s += max(a[i], 0);
            }
        }
        printf("%lld\n", max(res, s));
    }
    return 0;
}