#include<bits/stdc++.h>
using namespace std;
struct f{
    int q,c;
}a[100005];
bool cmp(f x,f y){
    return x.c<y.c;
}
int main(){
    int n,s;
    cin>>n>>s;
    for(int i=1;i<=n;i++){
        cin>>a[i].q>>a[i].c;
    }
    sort(a+1,a+n+1,cmp);
    if(a[n].c==a[n-1].c)cout<<a[n].c*s;
    else cout<<a[n-1].c*s+(a[n].c-a[n-1].c)*a[n].q;
    return 0;
}