#include <bits/stdc++.h> using namespace std; int main (){ int n,a,b,min1; cin>>n; cin>>a>>b; sum1+=a*b; min1=b; for(int i=1;i<=n;i++){ cin>>a>>b; if(b<min1)min1=b; sum1+=a*min1; } cout<<sum1; return 0; }