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

def remainder(V):
    x = 0; d = 1
    for X, Y in V:
        g, a, b = extgcd(d, Y)
        x, d = (Y*b*x + d*a*X) // g, d*(Y // g)
        x %= d
    return x, d


N = int(input())
V = [list(map(int, input().split())) for i in range(N)]

x, d = remainder(V)

for X, Y in V:
    if x % Y != X:
        print(-1)
        exit(0)
MOD = 10**9 + 7
if x == 0:
    print(d % MOD)
else:
    print(x % MOD)