#include <bits/stdc++.h>
using namespace std;


/* macro */
#define rep(i,a,b) for(int i=a;i<b;i++)
#define revrep(i,a,b) for(int i = a; i > b; i--)
#define int long long
#define exist(s,e) ((s).find(e)!=(s).end())
#define all(v) (v).begin(), (v).end()
#define each(s,itr) for(auto (itr) = s.begin(); (itr) != s.end(); (itr)++)
#define sum(v) accumulate(all(v), (0LL))


/* alias */
typedef vector<int> vi;
typedef pair<int, int> pi;


/* constant */
const int inf = 100100100100100100;
const int mod = 1e9;
int dx[8]={1,0,-1,0,-1,1,-1,1};
int dy[8]={0,1,0,-1,-1,-1,1,1};


/* io_method */
int input(){int tmp;cin >> tmp;return tmp;}
string raw_input(){string tmp;cin >> tmp;return tmp;}
string readline(){string s;getline(cin, s);return s;}
template<class T> void printx(T n){cout << n;}
template<class T, class U> void printx(pair<T, U> p){cout << "(" << p.first << "," << p.second << ")";}
template<class T> void printx(vector<T> v){cout << "{";rep(i,0,v.size()){printx(v[i]);if(i != v.size()-1)printx(",");}cout << "}";}
template<class T> void print(T n){printx(n);cout << endl;}
template<class T> void print(set<T> s){cout << "{";each(s, e){if(e != s.begin()) printx(",");printx(*e);}cout << "}" << endl;}
template<class T, class U> void print(map<T, U> mp){cout << "{";each(mp, e){cout << "(" << e -> first << "," << e -> second << ")";}cout << "}" << endl;}


/* general_method */
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
vector<int> cs(vector<int> arr){vector<int> tmp;if(arr.size() == 0) return tmp;tmp.push_back(arr[0]);rep(i,1,arr.size()){tmp.push_back(tmp.back() + arr[i]);}return tmp;}



/* main */
int n, p; 
vector<vi> arr(5000,vi());
double dp[5000][15000];

double dfs(int i, int solved, int point){

    if(dp[i][solved] > -1) return dp[i][solved];

    if(i == n){
        if(solved == p){
            return point / (n * 1.0);
        }else{
            return 100000000.0;
        }
    }

    double ans = 10000000.0;

    rep(j,0,4){
        chmin(ans, dfs(i + 1, solved + j, point + arr[i][j]));
    }

    return dp[i][solved] = ans;

}


signed main(){

    cin.tie(0);
    ios::sync_with_stdio(false);


    
    cin >> n >> p;

    

    rep(i,0,n){
        rep(j,0,3){
            arr[i].push_back(input());
        }
        arr[i].push_back(1);
    }



    memset(dp, -1, sizeof(dp));

    printf("%5f\n", dfs(0,0,0));















}