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 ABCI in ABC:
    cnt2 = min(cnt + 3, P + 1)
    for k in reversed(range(cnt2)):
        tmp = dp[k] + ABCI[0]
        for j in range(1,4):
            if 0 <= k - j < cnt:
                t1 = dp[k-j] + ABCI[j]
                if tmp > t1:
                    tmp = t1
        dp[k] = tmp
    cnt = cnt2
print(dp[P] / N)