#include <stdio.h>

int main(void) {
    int n;
    while (scanf("%d", &n) , n != -1) {
        int dist = 0, time = 0;
        while (n--) {
            int a, b;
            scanf("%d%d", &a, &b);
            dist += (b - time) * a;
            time = b;
        }
        printf("%d miles\n", dist);
    }
}