import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def SI(): return sys.stdin.readline()[:-1]

# a % y0 = x0
# a % y1 = x1
# a = y0 * p + x0
# a = y1 * q + x1
# まとめて
# y0 * p + x0 = y1 * q + x1
# y0 * p - y1 * q = x1 - x0

# a = lcm(y0,y1)*r + (y0 * p + x0)

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

md = 10 ** 9 + 7
def main():
    n = II()
    x1, y1 = MI()
    for _ in range(n - 1):
        x2, y2 = MI()
        p, q, g = extgcd(y1, -y2, x2 - x1)
        if (x2 - x1) % g:
            print(-1)
            exit()
        x1 = y1 * p + x1
        y1 = y1 * y2 // g
        x1 %= y1
    ans = (x1 - 1) % y1 + 1
    print(ans % md)

main()