#include <iostream>
#include <fstream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <cstring>
#include <string>
#include <cmath>
#include <iomanip>

using namespace std;

ifstream in("tunel.in");
ofstream out("tunel.out");

const long double EPS = 0.0000001;

int main() {

    int n, m;
    in >> n >> m;
    vector<vector<long double>> v(n + 1, vector<long double> (n + 2, 0));
    vector<vector<pair<int, int>>> g(n + 1);
    for(int i = 1; i <= m; i ++) {
        int a, b, c;
        in >> a >> b >> c;
        g[a].push_back({b, c});
        g[b].push_back({a, c});
    }

    v[n][n] = 1;
    for(int i = 1; i < n; i ++) {
        v[i][i] = g[i].size();
        for(auto it : g[i]) {
            v[i][it.first] --;
            v[i][n + 1] += it.second;
        }
    }

    int i = 1, j = 1;
    while(i <= n && j <= n) {

        int k;
        for(k = i; k <= n; k ++)
            if(v[k][j] < -EPS || v[k][j] > EPS)
                break;
        // j este variabila libera
        if(k == n + 1) {
            j ++;
            continue;
        }

        if(k != i)
            swap(v[i], v[k]);

        for(int l = j + 1; l <= n + 1; l ++)
            v[i][l] /= v[i][j];
        v[i][j] = 1;

        for(int u = i + 1; u <= n; u ++) {
            for(int l = j + 1; l <= n + 1; l ++)
                v[u][l] -= (v[u][j] * v[i][l]);
            v[u][j] = 0;
        }

        i ++;
        j ++;
    }

    vector<long double> x(n + 1, 0);
    for(int i = n - 1; i >= 1; i --) {
        for(int j = 1; j <= n + 1; j ++) {
            if(v[i][j] > EPS || v[i][j] < -EPS) {

                x[j] = v[i][n + 1];
                for(int k = j + 1; k <= n; k ++)
                    x[j] -= (x[k] * v[i][k]);

                break;
            }
        }
    }

    out << setprecision(10) << fixed << x[1];

    return 0;
}