#include<bits/stdc++.h>

using namespace std;
int main(){
    long long n,s,min=999999999,sum=0;
    long long a[2000000000][1000000005]={0};
    cin>>n>>s;
    for(long i=1;i<=n;i++){
        cin>>a[1][i]>>a[2][i];
        if(min>a[2][i]) {
        	min=a[2][i];
		}
    }
    for(long i=1;i<=n;i++){
        sum+=a[1][i]*(a[2][i]-min);
    }
    sum+=min*s;
    cout<<sum;
    return 0;
}