> #include<iostream>
> using namespace std;
> int main(){
> 	int a,b,tot,n,last;
> 	cin>>n;
> 	while(n!=-1)
> 	{
> 		last=tot=0;
> 		for(int i=0;i<n;i++)
> 		{
> 			cin>>a>>b;
> 			tot=tot+(b-last)*a;
> 			last=b;
> 		}
> 		cout<<tot<<" miles"<<endl;
> 		cin>>n;
> 	}
> 	return 0;
> }
哦