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;
}