M = 10 ** 9 + 7
I = [1, 1]
F = I[:]
R = I[:]
n = int(input()) - 1
for i in range(2, n + 1):
    z = (M - M // i) * I[M % i] % M
    I.append(z)
    F.append(i * F[-1] % M)
    R.append(z * R[-1] % M)
r = len(set(map(min, [map(int, input().split()) for _ in range(n)])))
print(1 if r < 1 else F[n]**2 * R[r] * R[n - r] * R[r - 1] * R[n - r + 1] * I[n] % M)