N, M = map(int, input().split())
card = [list(map(int, input().split())) for _ in range(N*M)]

IDX = [[-1]*N for _ in range(M)]
for i, (n, m) in enumerate(card):
    IDX[m-1][n-1] = i

def func(A):
    now = -1
    idx = 0
    cnt = 0
    while idx < 5:
        RANGE = A[idx]-now-1
        c = RANGE//(5-idx)+1
        cnt += c
        now += (5-idx)*c
        while idx < 5 and A[idx] <= now:
            idx += 1
    return cnt-1

ans = 10**18
for i in range(M):
    for j in range(N-5+1):
        A = sorted(IDX[i][j:j+5])
        ans = min(ans, func(A))
    ans = min(ans, func(sorted([IDX[i][0]]+IDX[i][-4:])))

print(ans)