func_code_string: #include <bits/stdc++.h>   using namespace std;   static const int mxn = 21;   long long n, res;   int m;   struct Node {     long long a;     int b;     bool operator<(const Node& c) const { return b > c.b; }   } nodes[mxn];   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     cin >> n >> m;     for (int i = 1; i <= m; ++i) {       cin >> nodes[i].a >> nodes[i].b;     }     sort(nodes + 1, nodes + 1 + m);     for (int i = 1; i <= m; ++i) {       if (n >= nodes[i].a) {         res += nodes[i].a * nodes[i].b;         n -= nodes[i].a;       } else {         res += n * nodes[i].b;         break;       }     }     cout << res <<   n ;     return 0;   }   