#include<bits/stdc++.h>
using namespace std;

using ll=long long;
const int N=1e5+9;
ll n,s,pre[N],ans,tuanti;
struct node
{
	ll p,c;
	bool operator<(const node &i)const
	{
		return c<i.c;
	}
}a[N];

int main()
{
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	cin>>n>>s;
	for(int i=1;i<=n;i++)cin>>a[i].p>>a[i].c;
	sort(a+1,a+1+n);
	for(int i=n;i>=1;i--)pre[i]=pre[i+1]+a[i].p;
	//for(int i=1;i<=n;i++)cout<<pre[i]<<' ';cout<<'\n';
	
	for(int i=1;i<=n;i++)
	{
		if(tuanti==a[i].c)continue;
		if(s<=pre[i])
		{
			ans+=(a[i].c-tuanti)*s;
			tuanti=a[i].c;
		}else if(s>pre[i])
		{
			ans+=(a[i].c-tuanti)*a[i].p;
			//tuanti=a[i].c;
		}
	}
	cout<<ans<<'\n';
	return 0;
}
/*Ac
*/