import java.util.*;

public class Main {
    static int[][] prises;
    static int[][] dp;
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p = sc.nextInt();
		prises = new int[3][n + 1];
		dp = new int[p + 1][n + 1];
		for (int i = 1; i <= n; i++) {
		    for (int j = 0; j < 3; j++) {
		        prises[j][i] = sc.nextInt();
		    }
		}
		double sum = dfw(p, n);
		System.out.println(sum / n);
	}
	
	static int dfw(int point, int idx) {
	    if (point < 0) {
	        return Integer.MAX_VALUE / 2 + 1;
	    }
	    if (idx == 0) {
	        return 0;
	    }
	    if (dp[point][idx] != 0) {
	        return dp[point][idx] ;
	    }
	    int min = dfw(point - 3, idx - 1) + 1;
	    for (int j = 0; j < 3; j++) {
	        min = Math.min(min, prises[j][idx] + dfw(point - j, idx - 1));
	    }
	    dp[point][idx] = min;
	    return min;
	}
}