#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdint>

using namespace std;

constexpr long long inf = 1e15;

int main()
{
	int n, p;
	cin >> n >> p;

	vector<vector<uint_fast64_t>> rank(n, vector<uint_fast64_t>(4, 1));
	for(auto& x : rank) {
		cin >> x[0] >> x[1] >> x[2];
	}

	vector<vector<uint_fast64_t>> dp(2, vector<uint_fast64_t>(p + 1, inf)); 
	for(auto i = 0; i < 4 && i <= p; ++i) {
		dp[1][i] = rank[0][i];
	}
	for(auto i = 2; i <= n; ++i) {
		for(auto j = 0; j <= p; ++j) {
			uint_fast64_t temp1 = dp[(i - 1) & 1][j] + rank[i - 1][0];
			uint_fast64_t temp2 = j > 0 ? dp[(i - 1) & 1][j - 1] + rank[i - 1][1] : inf;
			uint_fast64_t temp3 = j > 1 ? dp[(i - 1) & 1][j - 2] + rank[i - 1][2] : inf;
			uint_fast64_t temp4 = j > 2 ? dp[(i - 1) & 1][j - 3] + rank[i - 1][3] : inf;
			dp[i & 1][j] = min({temp1, temp2, temp3, temp4});
		}
	}

	cout << 1.00000 * dp[n & 1][p] / n << endl;

	return 0;
}