poj 2393

#include <iostream>
#include <cstring>
#include <cstdio>
#define MAX_N 10000

using namespace std;

//input
int N,S;
int Y[MAX_N],C[MAX_N];

//input
long long  ans = 0;             //可能会超过int

void solve(){
    for(int i = 0;i < N; i++){
        if(Y[i+1] - Y[i] > S){          //如果可以把下周的酸奶存储
            ans += ((Y[i] * C[i])+(Y[i] + S)*C[i+1]);       //加上存储的费用
            i++;                                    //周期加一
        }else{
            ans += Y[i] * C[i];
        }
    }
    printf("%I64d\n",ans);

}

int main()
{
    memset(Y,0,sizeof(Y));
    memset(C,0,sizeof(C));
    scanf("%d%d",&N,&S);
    for(int i = 0;i < N; i++){
        scanf("%d%d",&Y[i],&C[i]);
    }

    solve();

    return 0;
}