INF = 1e9
n,p = map(int,input().split())
dp = [[INF]*(p+1),[INF]*(p+1)]
dp[0][p] = 0
for i in range(n):
    abc = list(map(int,input().split()))
    abc.append(1)
    for j in range(p+1):
        dp[(i+1)%2][j] = INF
    for j in range(p+1):
        for k in range(4):
            if j >= k:
                dp[(i+1)%2][j-k] = min(dp[(i+1)%2][j-k],dp[i%2][j] + abc[k])
print(dp[n%2][0]/n)