```cpp
#include <bits/stdc++.h>
using namespace std;
struct milk{
int a,b;
}a[1000001];
bool cmp(milk x,milk y){
return x.a<y.a;
}
int main(){//因为N范(shu)围(ju)很(hen)小(shui)
int n,m;
cin>>m>>n;
for(int i=1;i<=n;i++){
cin>>a[i].a>>a[i].b;
}
sort(a+1,a+n+1,cmp);
int sum=0;
for(int i=1;i<=n;i++){
for(int j=1;j<=a[i].b;j++){
m--;
//cout<<m<<endl;
sum+=a[i].a;
if(m<=0)break;
}
if(m<=0)break;
}
cout<<sum<<endl;
}
```
竟然不爆炸了！
by WSZZ666 @ 2022-11-04 20:58:42