poj2017 speed limit

#include<iostream>
using namespace std;
int main(){
int n,sum,speed,total,cur;
while(cin>>n&&n!=-1){
sum=0;
cur=0;
while(n--){
cin>>speed>>total;
sum+=speed*(total-cur);
cur=total;
}
cout<<sum<<" miles"<<endl;
}
//system("pause");
return 0;
}