#include <bits/stdc++.h>   using namespace std;   const int MX = 1e5 + 3;   int t;   long long m, n;   pair<long long, long long> v[MX];   long long p[MX];   int main() {     scanf( %d , &t);     while (t--) {       scanf( %lld %lld , &n, &m);       long long ans = 0;       for (int i = 0; i < m; i++) {         scanf( %lld %lld , &v[i].first, &v[i].second);       }       sort(v, v + m, greater<pair<long long, long long>>());       for (int i = 0; i < m; i++) {         p[i] = v[i].first + (i ? p[i - 1] : 0);         if (i < n) ans += v[i].first;       }       for (int i = 0; i < m; i++) {         int l = 0;         int r = m - 1;         int md;         while (l != r) {           md = (l + r) / 2;           if (v[md].first < v[i].second)             r = md;           else             l = md + 1;         }         int cnt = l;         if (v[m - 1].first >= v[i].second) cnt++, l++;         long long sum = 0;         if (l) sum = p[l - 1];         if (l > i && cnt) {           cnt--;           sum -= v[i].first;         }         if (cnt > n - 2) {           continue;         }         long long ret = v[i].first + v[i].second * (n - cnt - 1) + sum;         ans = max(ans, ret);       }       printf( %lld n , ans);     }     return 0;   }   