POJ 2394 Yogurt factory 贪心

维护前i个星期是哪个的花费最少（包括储存的费用） minv=min(minv,C_i)

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb(a) push(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {
    return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {
    return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#else

    freopen("in.txt","r",stdin);
    //freopen("d:\\out1.txt","w",stdout);
#endif
}
int getch() {
    int ch;
    while((ch=getchar())!=EOF) {
        if(ch!=' '&&ch!='\n')return ch;
    }
    return EOF;
}

int main()
{
    int n,s;
    while(scanf("%d%d",&n,&s)!=EOF)
    {
        ll res=0;
        int minv=INF;
        for(int i=0;i<n;i++)
        {
            int a,b; scanf("%d%d",&a,&b);
            minv=min(minv+s,a);
            res=res+minv*b;
        }
        printf("%I64d\n",res);
    }
    return 0;
}