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| #include <bits/stdc++.h>
using namespace std;
const int LEN = 2e6 + 10;
struct Node
{
int p_, a_;
} arr[LEN];
int main()
{
int n, m;
cin >> n >> m;
for (int i = 0; i < m; ++i)
cin >> arr[i].p_ >> arr[i].a_;
sort(arr, arr + m, [](Node &a, Node &b) -> bool
{ return a.p_ < b.p_; });
int ans = 0;
for (int i = 0; i < m; ++i)
{
if (n >= arr[i].a_)
{
ans += arr[i].a_ * arr[i].p_;
n -= arr[i].a_;
}
else
{
ans += n * arr[i].p_;
break;
}
}
cout << ans;
return 0;
}
|