#include <iostream>
#include <algorithm>
using namespace std;
using i64 = long long;

constexpr int inf = 987654321;
int n, p;
vector<vector<int>> mat, dp;

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