#include<bits/stdc++.h>
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
#define pb push_back
int dy[]={0, 0, 1, -1, 1, 1, -1, -1};
int dx[]={1, -1, 0, 0, 1, -1, -1, 1};

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define mp make_pair
#define fi first
#define sc second
#define INF (1e9)

int N,P;
int a[4][5000];
int dp[5001][15001];

int main(){
	scanf("%d%d",&N,&P);
	REP(i,N) {
		scanf("%d%d%d",a[0]+i,a[1]+i,a[2]+i);
		a[3][i] = 1;
	}

	REP(j,P+1) {
		dp[N - 1][j] = (j < 4) ? a[j][N - 1] : INF;
	}

	RREP(i,N - 1) {
		REP(j,P+1) {
			int x[4];
			REP(k,4) 
				x[k] = INF;

			REP(k,4) {
				if(j > k - 1) {
					x[k] = dp[i + 1][j - k] + a[k][i];
				}
			}
			int y = INF;
			REP(k,4) {
				if(y > x[k]) 
					y = x[k];
			}
			dp[i][j] = y;
		}
	}

	
	printf("%0.10f\n",dp[0][P] / (double)N);
	return 0;
}