#include<bits/stdc++.h>
using namespace std;
#define vi vector<int>
#define vvi vector<vi>
#define vs vector<string>
#define pb push_back
#define P pair<int,int>
#define vp vector<P>
#define PP pair<P,int>
#define vpp vector<PP>
#define fi first
#define se second
#define INF 1e9
#define MOD 1000000007
#define REP(i,n) for(int i=0;i<n;i++)
#define REPR(i,n) for(int i=n;i>=0;i--)
#define FOR(i,m,n) for(int i=m;i<n;i++)
#define all(x) (x).begin(),(x).end()
int main(){
    int n,p;
    cin>>n>>p;
    vvi d(n,vi(4,1));
    REP(i,n){
        REP(j,3){
            cin>>d[i][j];
        }
    }
    vvi dp(n+1,vi(p+1,INF));

    dp[0][0]=0;
    REP(i,n){
        REP(j,p+1){
            REP(k,4){
                if(j+k<=p){
                    dp[i+1][j+k]=min(dp[i][j]+d[i][k],dp[i+1][j+k]);
                }
            }
        }
    }
    double ans=(double)dp[n][p]/(double)n;
    cout<<fixed<<setprecision(10)<<ans<<endl;
    return 0;
}