import logging
import sys
from inspect import currentframe

# 一つ前の配列だけ持っていれば十分
sys.setrecursionlimit(10 ** 6)
input = sys.stdin.readline

logging.basicConfig(level=logging.DEBUG)


def dbg(*args):
    id2names = {id(v): k for k, v in currentframe().f_back.f_locals.items()}
    logging.debug(
        ", ".join(id2names.get(id(arg), "???") + " = " + repr(arg) for arg in args)
    )


def main():

    INF = 10 ** 10
    n, p = map(int, input().split())
    dp = [[INF] * (p + 1) for _ in range(2)]
    dp[0][0] = 0
    for i in range(n):
        l = list(map(int, input().split()))
        l.append(1)
        for k in range(4):
            for j in range(p + 1):
                if j + k <= p:
                    dp[1][j + k] = min(dp[1][j + k], dp[0][j] + l[k])
        # for j in range(p + 1):
        #     dp[0][j] = dp[1][j]
        dp[0] = dp[1][:]
        dp[1] = [INF] * (p + 1)
    ans = dp[0][p] / n
    print(ans)


if __name__ == "__main__":
    main()