N, P = map(int, input().split())
ABC = [list(map(int, input().split())) + [1] for _ in range(N)]
INF = 10 ** 9
dp = [0] * (P + 1)
cnt = 1
for i in range(N):
    cnt2 = min(cnt + 3, P + 1)
    for k in reversed(range(cnt2)):
        tmp = INF
        for j in range(4):
            if 0 <= k - j < cnt2:
                tmp = min(tmp,dp[k-j] + ABC[i][j])
        dp[k] = tmp
    cnt = cnt2
print(dp[P] / N)