// https://infoarena.ro/problema/tunel

//#ifdef _MSC_VER
//	#define _CRT_SECURE_NO_WARNINGS
//#elif  __GNUC__
//	#pragma GCC optimize("Ofast,unroll-loops,inline")
//	#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
//#endif

//#define _USE_MATH_DEFINES

#include <iostream>
#include <fstream>
#include <utility>
#include <cstdint>
//#include <cstdio>
//#include <algorithm>
#include <vector>
//#include <array>
//#include <list>
//#include <forward_list>
//#include <string>
//#include <cstring>
//#include <cmath>
//#include <bitset>
//#include <queue>
//#include <stack>
//#include <map>
//#include <set>
//#include <unordered_map>
//#include <unordered_set>
//#include <limits>
//#include <climits>
#include <iomanip>
//#include <tuple>
//#include <numeric>
//#include <chrono>
//#include <memory>

using namespace std;

using int64 = int64_t;
using uint64 = uint64_t;
using int32 = int32_t;
using uint32 = uint32_t;
using int16 = int16_t;
using uint16 = uint16_t;
using pii = pair<int, int>;
using pll = pair<int64, int64>;

#define all(x) (x).begin(), (x).end()
#define allg(x) (x).begin(), (x).end(), greater<int>()
#define sz(x) (int)(x).size()
#define pb push_back
#define eb emplace_back
#define rfor(i, st, dr) for(auto i=(st); i<=(dr); ++i)
#define for0(i,n) for(auto i=0; i<(n); ++i)
#define rfor0(i,n) for(auto i=(n)-1; i>=0; --i)
#define for1(i,n) for(auto i=1; i<=(n); ++i)
#define rfor1(i,n) for(auto i=(n); i>=1; --i)
#define foreach(x,a) for(auto& x : a)
#define cforeach(x,a) for(const auto& x : a)
#define ft first
#define sd second
#define cendl cout << "\n"
#define fendl fout << "\n"
#define FASTIO ios::sync_with_stdio(false); cin.tie(nullptr);

//#define int int64

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

//FILE* fin = fopen("", "r");
//FILE* fout = fopen("", "w");

const int NRMAX = 255;
const double EPS = 1e-8;
const double ZERO = 0.000;

double mat[NRMAX + 5][NRMAX + 5];
double dist[NRMAX + 5];
bool viz[NRMAX + 5];
vector<pii> gr[NRMAX + 5];

void dfs(int x) {
	viz[x] = true;
	cforeach(it, gr[x]) {
		if (!viz[it.ft])
			dfs(it.ft);
	}
}

int32 main()
{
	//FASTIO;

	int n, m, a, b, c;

	fin >> n >> m;
	for1(i, m) {
		fin >> a >> b >> c;

		gr[a].eb(b, c);
		gr[b].eb(a, c);
	}

	// verific sa fie drum pana la final
	dfs(1);
	if (!viz[n]) {
		fout << ZERO << "\n";
		return 0;
	}

	// initializam matricea de ecuatie
	for (int i = 1; i < n; ++i) {
		mat[i][i] = sz(gr[i]);

		cforeach(it, gr[i]) {
			mat[i][it.ft] -= 1.0;
			mat[i][n + 1] += it.sd;
		}
	}
	mat[n][n] = 1.0;
	mat[n][n + 1] = 0.0;

	// eliminarea gaussiana 
	for (int r = 1; r <= n; ++r) {
		if (abs(mat[r][r]) <= EPS) { // daca e aprox 0
			// daca elementul de pe [r][r] e 0 atunci cautam un element nou
			// desi nu ar trebui sa se intample asta la problema asta cred ... 

			int i;

			for (i = r + 1; i <= n; ++i)
				if (!(abs(mat[i][r]) <= EPS))
					break;

			if (i > n) {
				continue;
			}

			swap(mat[r], mat[i]);
		}

		for (int i = 1; i <= n; ++i) { //  iau fiecare linie
			if (i == r)
				continue;

			double rp = mat[i][r] / mat[r][r];

			for (int j = r; j <= n + 1; ++j) // toate din inainte is deja 0
				mat[i][j] -= rp * mat[r][j];
		}
	}


	fout << setprecision(3) << fixed << mat[1][n + 1] / mat[1][1] << "\n";

	return 0;
}