#include <bits/stdc++.h>

using namespace std;

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

const int MMAX(5005), NMAX(105);
const double EPS(0.0000001);
struct chestie
{
    int a, b, c;
} v[MMAX];
int n, m;
double mat[NMAX][NMAX], sol[NMAX];

inline void Gauss()
{
    int i = 1, j = 1;
    while(i <= n && j <= n)
    {
        int k = i;
        for(; k <= n; ++k)
            if(mat[k][j] > EPS || mat[k][j] < -EPS)
                break;
        if(k == n + 1)
        {
            ++j;
            continue;
        }
        if(i != k)
            for(int c = 1; c <= n + 1; ++c)
            {
                double aux = mat[i][c];
                mat[i][c] = mat[k][c];
                mat[k][c] = aux;
            }
        for(int c = j + 1; c <= n + 1; ++c)
            mat[i][c] /= mat[i][j];
        mat[i][j] = 1;
        for(int u = i + 1; u <= n; ++u)
        {
            for(int c = j + 1; c <= n; ++c)
                mat[u][c] -= mat[i][c] * mat[u][j];
            mat[u][j] = 0;
        }
        ++i, ++j;
    }
    for(i = n; i >= 1; --i)
    {
        for(j = 1; j <= n + 1; ++j)
            if(mat[i][j] > EPS || mat[i][j] < - EPS)
            {
                if(j == n + 1){
                    sol[0] = -1;
                    return;
                }

                sol[j] = mat[i][n + 1];
                for(int k = j + 1; k <= n; ++k)
                    sol[j] -= sol[k] * mat[i][k];
                break;
            }
    }
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        fin >> v[i].a >> v[i].b >> v[i].c;
        if(v[i].a > v[i].b)
            swap(v[i].a, v[i].b);
        if(v[i].c == 0)
            continue;
        if(v[i].a != 1 && v[i].a != n)
        {
            mat[v[i].a][v[i].a]--;
            mat[v[i].a][v[i].b]++;
        }
        if(v[i].b != 1 && v[i].b != n)
        {
            mat[v[i].b][v[i].b]--;
            mat[v[i].b][v[i].a]++;
        }
    }
    mat[1][1] = 1;
    mat[n][n + 1] = 1;
    mat[n][n] = 1;

    Gauss();

    if(sol[0] == -1){
        fout << "0\n";
        return 0;
    }

    double rez = 2e9;
    for(int i = 1; i <= m; ++i){
        if(sol[v[i].a] < 0 || sol[v[i].b] < 0)
            continue;
        double dist = abs(sol[v[i].a] - sol[v[i].b]);
        rez = min(rez, v[i].c / dist);
    }
    double sum = 0;
    for(int i = 1; i <= m; ++i){
        if(v[i].b == n && sol[v[i].a] != sol[v[i].b])
            sum += rez * abs(sol[v[i].a] - sol[v[i].b]);
    }
    fout << fixed << setprecision(10) << sum << '\n';
    return 0;
}