from itertools import permutations
n, m = map(int, input().split())
P = [-1] * n
for _ in range(m):
  pi, ki = map(lambda x: int(x)-1, input().split())
  P[ki] = pi
ans = 0
for p in permutations(range(n)):
  flg = 0
  for i in range(n):
    if P[i] != -1 and p[i] != P[i]:
      flg = 1
  if flg:
    continue
  for i in range(n):
    for j in range(i+1, n):
      ans += p[i] > p[j]
print(ans)