def read_data():
    N, P = map(int, input().split())
    ranks = []
    for n in range(N):
        a, b, c = map(int, input().split())
        ranks.append([a, b, c])
    return N, P, ranks

def solve(N, P, ranks):
    '''
    N: コンテストの数
    P: Sum(x[i] for i in range(N))
    ranks[k][s]: k 番目のコンテストでs問解いたときの順位
    このとき、sum(ranks[i][x[i]]) の最小値を求めたい。
    dp[k][p]: k番目のコンテストまでで累積p問解いたときの順位合計の最小値
    
    dp[k][p] = min(dp[k-1][p]   + ranks[k][0],
                   dp[k-1][p-1] + ranks[k][1],
                   dp[k-1][p-2] + ranks[k][2],
                   dp[k-1][p-3] + 1)
    あるいは、
    dp[k][p] = min(dp[k][p], dp[k-1][p])
    '''
    dp = ranks[0] + [1]
    for k in range(1, N):
        rank0, rank1, rank2 = ranks[k]
        ndp = [dpi + rank0 for dpi in dp]
        ndp.extend([float('inf'), float('inf'), float('inf')])
        for i, dpi in enumerate(dp):
            ndp[i + 1] = min(ndp[i + 1], dpi + rank1)
            ndp[i + 2] = min(ndp[i + 2], dpi + rank2)
            ndp[i + 3] = min(ndp[i + 3], dpi + 1)
        dp = ndp
    return dp[P]/N

N, P, ranks = read_data()
print(solve(N, P, ranks))