Speed Limit

http://poj.org/problem?id=2017

#include<stdio.h>
int main()
{
    int n,mile,hour;
    while(~scanf("%d",&n)&&n!=-1)
    {
        int sum = 0,h = 0;
        while(n--)
        {
            scanf("%d%d",&mile,&hour);
            h = hour-h;
            sum += mile*h;
            h = hour;
        }
        printf("%d miles
",sum);
    }
    return 0;
}