N, M = map(int, input().split())
ind = [[None for i in range(M)] for j in range(N + 1)]
for i in range(N * M):
	n, m = map(int, input().split())
	if n == 1:
		ind[N][m - 1] = i
	ind[n - 1][m - 1] = i
ret = float('inf')
for i in range(N - 3):
	for j in range(M):
		temp = []
		for k in range(5):
			temp.append(ind[i + k][j])
		temp = sorted(temp)
		ans = 0
		cur = 4
		for k in range(5, 0, -1):
			if cur < temp[5 - k]:
				ans += (temp[5 - k] - cur + k - 1) // k
				cur += k * ((temp[5 - k] - cur + k - 1) // k)
		ret = min(ret, ans)
print(ret)