import std.algorithm, std.conv, std.range, std.stdio, std.string;

void main()
{
  auto rd = readln.split.to!(int[]), n = rd[0], p = rd[1];
  auto r = new int[][](n, 4);
  foreach (i; 0..n) r[i] = readln.split.to!(int[]) ~ 1;

  auto inf = 10^^9;
  auto dp = new int[][](n+1, p+1);
  foreach (i; 0..n+1) dp[i][] = inf;
  dp[0][0] = 0;

  foreach (i; 0..n)
    foreach (j; 0..p+1)
      foreach (k; 0..4)
        if (j-k >= 0)
          dp[i+1][j] = min(dp[i+1][j], dp[i][j-k] + r[i][k]);

  writefln("%.6f", dp[n][p].to!real / n);
}