随笔——CodeForces 588A Description

#include<cstdio>
#include<cstring>
#include<iostream>

using namespace std;

#define  MAX(x,y) (((x)>(y)) ? (x) : (y))
#define  MIN(x,y) (((x) < (y)) ? (x) : (y))
#define ABS(x) ((x)>0?(x):-(x))

const int inf = 0x7fffffff;

const int N=100000+10;
int a[N];
int b[N];
int main()
{
    int n;
    cin>>n;
    for(int i=0; i<n; i++){
        scanf("%d%d",a+i,b+i);
    }
    int cheap=0;
    int cnt=a[0];
    long long ans=0;
    for(int i=1; i<n; i++){
        if(b[i] < b[cheap] ){
            ans += b[cheap]*cnt;
            cnt=a[i];
            cheap=i;
        }
        else{
            cnt += a[i];
        }
//        cout<<"ans= "<<ans<<endl;
    }
    ans += b[cheap]*cnt;
    cout<<ans<<endl;
    return 0;
}