N, P = map(int, input().split())
INF = 10**10
dp = [[INF] * (P+1) for i in range(N+1)]
dp[0][0] = 0
for i in range(N):
    dp[i+1][:] = dp[i][:]
    scores = list(map(int, input().split())) + [1]    
    # 今まで解いた問題の合計 j
    for j in range(P+1):
        # if dp[i][j] == INF : continue
        # このコンテストで解いた問題数 k
        tmp = dp[i+1][j]
        score_j0 = dp[i][j]  + scores[0]
        tmp = score_j0 
        if j - 1 >= 0:
            score_j1 = dp[i][j-1] + scores[1]
            tmp = min(tmp, score_j1)
        if j - 2 >= 0:
            score_j2 = dp[i][j-2] + scores[2]
            tmp = min(tmp, score_j2)
        if j - 3 >= 0:
            score_j3 = dp[i][j-3] + scores[3]
            tmp = min(tmp, score_j3)
        dp[i+1][j] = tmp
print(dp[N][P]/N)