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

n = input()
d = 1
x = 0
v = []
for i in xrange(n):
    X, Y = map(int, raw_input().split())
    g, a, b = extgcd(d, Y)
    x, d = (Y*b*x + d*a*X)/g, d*(Y / g)
    x = (x + d) % d
    v.append((X, Y))

for X, Y in v:
    if x % Y != X:
        print -1
        exit(0)
print x