70分，RE#4#5，WA#10，求调，回者必关

#include<iostream>
#include<algorithm> 
#include<iomanip> 
#define int long long
using namespace std;
int n,s,ans;
struct node {
	int c,y;
}a[1005];
signed main(){
	cin>>n>>s;
	for(int i=1;i<=n;i++) {
		cin>>a[i].c>>a[i].y;
	}
	for(int i=1;i<=n;i++) {
		int t=a[i].c*a[i].y;
		int mi=t;
		for(int j=1;j<=i;j++) {
			int m=a[j].c*a[i].y+(i-j)*s*a[i].y;
			mi=min(mi,m);
		}
		ans+=mi;
	}
	cout<<ans;
   return 0;
}