#include <iostream>
#include <algorithm>
using namespace std;

constexpr int inf = 987654321;

int main(void) {
  int n, p; scanf("%d%d", &n, &p);
  vector<vector<int>> mat(4, vector<int>(n)); // mat[4][n]
  for(int i=0; i<n; ++i) {
    scanf("%d%d%d", &mat[0][i], &mat[1][i], &mat[2][i]);
    mat[3][i] = 1;
  }
  vector<vector<int>> dp(2, vector<int>(p+1, inf)); // dp[2][p+1]
  dp[0][0] = 0;
  for(int i=0; i<n; ++i) {
    int cur = i & 1,
        nxt = (i+1) & 1;
    for(int j=0; j<=p; ++j) {
      if(dp[cur][j] == inf) { continue; }
      for(int k=0; k<=3 && j+k<=p; ++k) {
        dp[nxt][j+k] = min(dp[nxt][j+k], dp[cur][j] + mat[k][i]);
      }
    }
    dp[cur].assign(p+1, inf);
  }
  int res = dp[n&1][p];
  double ave = double(res) / n;
  printf("%.10lf\n", ave);
  return 0;
}