N, M = map(int, input().split())
X = [[0] * N for _ in range(M)]
for i in range(N * M):
    n, m = map(int, input().split())
    X[m - 1][n - 1] = i
for i in range(M):
    X[i].append(X[i][0])

ans = N * M
for i in range(M):
    for j in range(N - 3):
        C = X[i][j:j + 5]
        C.sort()
        tmp = 0
        cnt = -1
        for k in range(5):
            if tmp > C[k]:
                continue
            else:
                tmp2 = - (-(C[k] - tmp + 1) // (5 - k))
                cnt += tmp2
                tmp += tmp2 * (5 - k)
        ans = min(ans, cnt)
print(ans)