/*  This Code is Submitted by wywcgs for Problem 1688 on 2005-03-05 at 15:55:07 */ 
#include <stdio.h>

int main()
{
    int speed[10] = {0}, time[10] = {0}, distance = 0;
    int n, i;
    
    while(scanf("%d", &n) == 1){
        if(n == -1){
            return 0;
        }else{
            for(i = 0; i < n; i++){
                scanf("%d %d", &speed[i], &time[i]);
                if(i == 0){
                    distance = speed[0] * time[0];
                }else{
                    distance += speed[i] * (time[i] - time[i-1]);
                }    
            }
            printf("%d miles\n", distance);
        }
    }

    return 0;
}