bzoj 1680: [Usaco2005 Mar]Yogurt factory【贪心】

贪心，一边读入一边更新mn，用mn更新答案，mn每次加s

#include<iostream>
#include<cstdio>
using namespace std;
int n,s,mn=1e9;
long long ans;
int main()
{
    scanf("%d%d",&n,&s);
    for(int i=1,w,c;i<=n;i++)
    {
        scanf("%d%d",&w,&c);
        mn+=s;
        mn=min(mn,w);
        ans+=1ll*mn*c;
    }
    printf("%lld\n",ans);
    return 0;
}