#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> PII;
const int N=100010;
ll res;
int main(){
    int n;
    ll s;
    cin>>n>>s;
    vector<PII> a;
    for(int i=1;i<=n;i++){
       ll x,c;
       cin>>c>>x;
       a.push_back({x,c});
       res+=c;
    }
    sort(a.begin(),a.end());
   // cout<<res<<endl;
    int l;
    for(int i=0;i<a.size();i++){
       if(res<=s){
          l=i;
         // cout<<res<<endl;
           break;
       }
       res-=a[i].second;
       //cout<<res<<endl;
    }
    ll r=a[l-1].first;
    ll ans=s*r;
    for(int i=l;i<n;i++){
       ans+=max(0ll,a[i].first-r)*a[i].second;
    }
    cout<<ans;
    return 0;
}