#include<bits/stdc++.h>
#define fastio ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define lli long long int
#define ulli unsigned long long int
#define ff first
#define ss second
#define mp make_pair
#define pb push_back
#define pf pop_front()
#define lb lower_bound
#define ub upper_bound
#define bs binary_search
#define loopl(i,a,b) for(lli i=a;i<b;i++) 
#define loop(i,a,b) for(int i=a;i<b;i++)
#define mod 1000000007
#define inf 1000000000000000
#define lld long double
#define pll pair<long long int,long long int>
#define vll vector<lli>
#define eps 0.000001
//#define endl '\n'

using namespace std ;

#define MAXN 100010
//lli spf[MAXN];  
//void sieve();
//set<lli> factors(lli x);
lli power(lli x,lli y,lli p);
//void getZarr(string str, lli Z[]);
//vll prefix_function(vll s); 

int main()
{


    lli n,m;
    cin>>n>>m;

    pll p[n];

    loopl(i,0,n)
    cin>>p[i].ff>>p[i].ss;

    sort(p,p+n);

    lli cnt=0,cost=0;

    loopl(i,0,n)
    {
        if(m - cnt > p[i].ss)
        {
            cost+=p[i].ff*p[i].ss;
            cnt+=p[i].ss;
        }

        else
        {
            cost+=p[i].ff*(m-cnt);
            cnt=m;
            break;
        }
    }

    cout<<cost<<endl;


}


/*vll prefix_function(vll s) 
{
    lli n = (lli)s.size();
    vll pi(n);
    
    for (lli i = 1; i < n; i++)
    {
        lli j = pi[i-1];
        
        while (j > 0 && s[i] != s[j])
            j = pi[j-1];
        
        if (s[i] == s[j])
            j++;
        
        pi[i] = j;
    }
    return pi;
}
*/
/*void sieve() 
{ 
    spf[1] = 1; 
    loopl(i,2,MAXN) 
        spf[i] = i; 
    for (lli i=4; i<MAXN; i+=2) 
        spf[i] = 2; 
  
    for (lli i=3; i*i<MAXN; i++) { 
        if (spf[i] == i) { 
            for (lli j=i*i; j<MAXN; j+=i) 
                if (spf[j]==j) 
                    spf[j] = i; 
        } 
    }

} 

multiset<lli> factors(lli x) 
{ 
    multiset<lli> pr; 
    while (x != 1) 
    { 
        pr.insert(spf[x]); 
        x = x / spf[x]; 
    } 
    return pr; 
}

*/

/*
void dfs(lli q,lli root) 
{
    vis[q]=1;
    
    ans[q]=1;

    for(auto x: v[q])
    {
        if(!vis[x])
        {
            if(a[x]==a[root] && x<root) continue;
            if(a[x]<a[root] || a[x]>a[root]+d) continue;
            dfs(x,root);
            ans[q]=(ans[q]*((ans[x]+1)%mod))%mod ;
        }
    }
        
}
*/



/*void getZarr(string str, lli Z[])
{
    lli n = str.length();
    lli L, R, k;
    L = R = 0;
    for (lli i = 1; i < n; ++i){
        if (i > R){
            L = R = i;
            while (R<n && str[R-L] == str[R])
                R++;
            Z[i] = R-L;
            R--;
        } else {
            k = i-L;
            if (Z[k] < R-i+1)
                Z[i] = Z[k];
            else {
                L = i;
                while (R<n && str[R-L] == str[R])
                    R++;
                Z[i] = R-L;
                R--;
            }
        }
    }
}


*/

lli power(lli x, lli y, lli p) 
{ 
    lli res = 1;   
    x = x % p;  
    while (y > 0) 
    { 
        if (y & 1) 
            res = (res*x) % p; 
  
        y = y>>1;  
        x = (x*x) % p;   
    } 
    return res; 
} 


Measured memory_bytes: 1792