function Main(input) {

  let inputs = input.split('\n');

  let n, p;
  [n, p] = inputs[0].split(' ').map((e) => e - 0);

  let a = new Array(n);
  let b = new Array(n);
  let c = new Array(n);

  for (let i = 0; i < n; ++i) {
    [a[i], b[i], c[i]] = inputs[1 + i].split(' ').map((e) => e - 0);
  }

  let dp = new Array(2);
  dp[0] = new Array(p + 1).fill(10**9);
  dp[0][0] = 0;
  for (let i = 0; i < n; ++i) {
    dp[~i & 1] = new Array(p + 1).fill(10**9);
    for (let j = 0; j <= p; ++j) {
      dp[~i & 1][j] = Math.min(dp[~i & 1][j], dp[i & 1][j] + a[i]);
      if (j + 1 <= p) {
        dp[~i & 1][j + 1] = Math.min(dp[~i & 1][j + 1], dp[i & 1][j] + b[i]);
      }
      if (j + 2 <= p) {
        dp[~i & 1][j + 2] = Math.min(dp[~i & 1][j + 2], dp[i & 1][j] + c[i]);
      }
      if (j + 3 <= p) {
        dp[~i & 1][j + 3] = Math.min(dp[~i & 1][j + 3], dp[i & 1][j] + 1);
      }
    }
  }

  console.log('%s', (dp[n & 1][p] / n).toFixed(7));

}

Main(require('fs').readFileSync('/dev/stdin', 'utf8'));