def extgcd(a, b):
    if b == 0:
        return (a, 1, 0)
    (g, y, x) = extgcd(b, a % b)
    return (g, x, y - (a // b) * x)



N = int(raw_input()) - 1
ans, add = map(int,raw_input().strip().split());
if ans == 0:
    ans = ans + add

while N > 0:
    X, Y = map(int,raw_input().strip().split())
    g, a, b = extgcd(add, Y)
    now = ans % Y
    need = X - now
    if need < 0:
        need = need + Y
    if need % g != 0:
        ans = -1;
        break
    need = need / g
    ans = ans + (add * a) * need
    add = add * Y / g
    ans = ans % add
    if ans < 0:
        ans = ans + add

print(ans)