N = int(input())
K = tuple([tuple(map(int, input().split(' '))) for i in range(int(input()))])
count = 0
l = [i for i in range(1, N + 1)]
while True:
    for x, y in K:
        l[x - 1], l[y - 1] = l[y - 1], l[x - 1]
    count += 1
    for j, n in enumerate(l):
        if j + 1 != n:
            break
    else:
        break

print(count)