#include <cstdio>
#include <cassert>
#include <algorithm>
using namespace std;
typedef long long ll;

#define N 10005
int n; 
ll m;
pair<ll,ll> pds[N];

int main() {
  while(scanf("%d%lld",&n,&m),n|m) {
    assert(1<=n&&n<=10000);
    assert(0<=m&&m<=1000000000);
    for (int i=0;i<n;++i) {
      scanf("%lld%lld",&pds[i].second,&pds[i].first);
      assert(1<=pds[i].second&&pds[i].second<=10000);
      assert(0<=pds[i].first&&pds[i].first<=10);
    }
    sort(pds,pds+n);
    reverse(pds,pds+n);
    for (int i=0;i<n&&m>0;++i) {
      int use=min(pds[i].second,m);
      pds[i].second-=use;
      m-=use;
    }
    ll ans=0;
    for (int i=0;i<n;++i) ans+=pds[i].first*pds[i].second;
    assert(0<=ans&&ans<=INT_MAX);
    printf("%lld\n",ans);
  }
}