// yukicoder: No.472 平均順位
// bal4u 2019.8.20

#include <stdio.h>
#include <string.h>

//// 入出力関係
#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() { // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

int dp[2][15005];
		
int main()
{
	int i, j, k, p, q, ma, a[4], N, P;

	N = in(), P = in();
	memset(dp[0], 0x33, sizeof(dp[0]));
	ma = 0, dp[0][0] = 0, a[3] = 1;
	p = 0, q = 1;
	for (i = 0; i < N; i++) {
		memset(dp[q], 0x33, sizeof(dp[0]));
		for (j = 0; j <= 2; j++) a[j] = in();
		for (j = 0; j <= 3; j++) {
			for (k = ma; k >= 0; k--) {
				if (dp[p][k] + a[j] < dp[q][k+j]) dp[q][k+j] = dp[p][k] + a[j];
			}
		}
		if (ma < P) ma += 3;
		p = q, q = !q;
	}
	printf("%.8lf\n", (double)dp[p][P]/N);
	return 0;
}