POJ 1017:Packets

#include <iostream>
#include <stdio.h>

using namespace std;

const int MAX_N=10000;

long long c[10001];
long long y[10001];
long long n,s;
long long sum;

int main()
{
freopen("in.txt","r",stdin);
cin>>n>>s;
sum=0;
long long minc;
for(int i=0;i<n;i++)
{
cin>>c[i]>>y[i];
minc=minc+s;
if(c[i]<minc)
minc=c[i];
sum=sum+y[i]*minc;
}
cout<<sum;
return 0;
}