# K : 桁数
N = int(input())
R = {}
for i in range(N):
    l, r  = map(int, input().split())
    R[i] = [l, r]

K = N
Q = []
for i in range(2**(K)):
    T =[]
    bs = format(i, f'0{K}b')   # K桁の２進数の数
    for j in range(K):
        T.append( [j, R[j][int(bs[j])]])

    sT = sorted(T, key=lambda x:x[1])
    q =''
    for j in range(K):
        q += str(sT[j][0])
    Q.append(q)

Q = set(Q)
print(len(Q))