#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<map>
#include<stack>
#include<cmath>
#include<iomanip>
#include<set>
#include<numeric>
#include<sstream>
#include<random>
#include<cassert>
#include<climits>
#include<cstring>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rrep(i, st, n) for (int i = st; i < n; ++i)
using pii = pair<int, int>;
const int inf = 1e9 + 7;
int dy[] = {0, 0, -1, 1, -1, 1, -1, 1};
int dx[] = {1, -1, 0, 0, -1, 1, 1, -1};
#define ceil(a, b) a / b + !!(a % b)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)

int v[5000][4], n;
int memo[5000][15001];
int dfs(int d, int r){
    if (d == n) return 0;
    if (!memo[d][r]){
        memo[d][r] = inf;
        //int rem = (n - d) * 3;
        /*if ( rem >= r)*/
        for (int i = 0; i <= (r < 3 ? r : 3); i++) chmin(memo[d][r], dfs(d + 1, r - i) + v[d][i]);
    }
    return memo[d][r];
}
int main(){
    int k;
    cin >> n >> k;
    for(int i = 0; i < n; v[i][3] = 1, i++) rep(j, 3) cin >> v[i][j];
    cout << dfs(0, k) * 1.0 / n << endl;
}