zoj 2176 Speed Limit

#include<stdio.h>

int main(){
	int sp,n,tm,mile,tmp;
	while(scanf("%d",&n)&&n>=0){
		mile = 0;
		tmp = 0;
		while(n--){
			scanf("%d%d",&sp,&tm);
			mile += sp*(tm - tmp);
			tmp = tm;
		}
		printf("%d miles\n",mile);
	}

return 0;
	}