# include<iostream> # include<cstring> # include<cstdio> using namespace std; int main(){ int n=0,i=0,a,b,num=0,min=101; cin>>n; for(int i=0;i<n;i++){ cin>>a>>b; if(min>b) min=b; num+=a*min; }cout<<num<<endl; return 0; }