#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>
#define pii pair<int,int>
#define x first
#define y second
#define mp make_pair
    
using namespace std;
    
ifstream cin("retea.in");
ofstream cout("retea.out");

const double eps = 1e-5;
const int NMAX = 1001;
int N, M, K;
double dist[1<<14];
double edge[int(1e5)];
vector<int> G[NMAX];
priority_queue< pair< double ,int> > Q;

inline bool comp(const double &a,const double b) {
	return a - b > eps;
}
    
inline void readData() {
    cin>>N>>M>>K;
    for(int a, b, c, e = 0;e < M;e++) {
        cin>>a>>b>>c;
        G[a].push_back(b + (e<<10));
        G[b].push_back(a + (e<<10));
        edge[e] = 1.0*c/(1<<K);
    }
}
    
inline void djikstra() {
    for(int i = 1;i <= N;i++) {
        for(int j = 0;j <= K;j++) {
            dist[i | j<<10] = int(2e9)*1.0;
        }
    }
    dist[1] = 0;
    Q.push(mp(0,1));
    double c;
    int ww, e;
    while(!Q.empty()) {
        int V = Q.top().y;
        int v = V & 1023, k = V>>10;
		if (v == K && k == K) break;
        Q.pop();
        for(const int &w : G[v]) {
            ww = w & 1023;
            e = w>>10;
            c = 1ll*edge[e]*(1ll<<k);
            for(int j = K;j >= k;j--, c *= 2.0) {
                if(comp(dist[ww | j<<10] ,dist[V] + c)) {
                    dist[ww | j<<10] = dist[V] + c;
                    Q.push(mp(-dist[ww | j<<10],ww | j<<10));
                }
            }
        }
    }
}
    
    
int main()
{
    readData();
    djikstra();
    cout.precision(4);
    cout<<fixed<<1.0*dist[N | K<<10];
    return 0;
}