#include <iostream>

using namespace std;

int main()
{
    int n,i,a,b,min,s=0,v=0;
    cin>>n;
    cin>>a;
    cin>>b;
    min=b;
    v=v+min*a;
    for (i=1;i<n;i++)
    {
        cin>>a;
    cin>>b;
        if (min<=b)
        {
        v=v+a*min;
        }
        else if (min>b)
        {
        min=b;
        v=v+min*a;
        }
    }
    cout<<v;
    return 0;
}