[백준/파이썬]14541번 Speed Limit

while 1:
    t = int(input())
    time = time2 = 0
    r = 0
    if t == -1:
        break
    for i in range(t):
        n = list(map(int, input().split()))
        time = n[1] - time2
        time2 = n[1]
        r += n[0] * time
    print(r, "miles")