#include<bits/stdc++.h> using namespace std; struct heka{ int price; int num; }a[100]; bool cmp(heka a,heka b){ if(a.price<b.price) { return true; } else { return false; } } int main() { int n,m; cin>>m>>n; for(int i=0;i<n;i++){ cin>>a[i].price>>a[i].num; } sort(a,a+n,cmp); int sum=0,price=0; for(int i=0;i<n;i++){ sum+=a[i].num; price+=(a[i].num*a[i].price); if(sum>m){ price-=(sum-m)*a[i].price; break; } } cout<<price; return 0; }