#include <fstream>
#include <vector>
#include <iomanip>

using namespace std;

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

const int NMAX = 255;
const long double EPS = 1e-8;

int N, M;
vector < pair <int, int> > g[NMAX + 5];

long double sys[NMAX + 5][NMAX + 5];
long double ans[NMAX + 5];

bool NotNull(long double X)
{
    return (X < -EPS || X > EPS);
}

int main()
{
    fin >> N >> M;

    for(int i = 1; i <= M; i++)
    {
        int x, y, z;
        fin >> x >> y >> z;

        g[x].push_back({y, z});
        g[y].push_back({x, z});
    }

    for(int i = 1; i < N; i++)
    {
        sys[i][i] = (long double)g[i].size();

        int sum = 0;

        for(auto it : g[i])
        {
            sys[i][it.first] -= (long double)1;
            sum += it.second;
        }

        sys[i][N + 1] = (long double)sum;
    }

    int l = 1, c = 1;

    while(l <= N && c <= N)
    {
        int k;

        for(k = l; k <= N; k++)
            if(NotNull(sys[k][c]))
                break;

        if(k == N + 1) ///variabila libera, ii dam valoarea 0
        {
            c++;
            continue;
        }

        ///swap la liniile l, k

        for(int j = 1; j <= N + 1; j++)
            swap(sys[l][j], sys[k][j]);

        for(int j = c + 1; j <= N + 1; j++)
            sys[l][j] /= sys[l][c];

        sys[l][c] = (long double)1;

        for(int i = l + 1; i <= N; i++)
        {
            for(int j = c + 1; j <= N + 1; j++)
                sys[i][j] -= sys[i][c] * sys[l][j];

            sys[i][c] = 0;
        }

        l++, c++;
    }

    for(int i = N; i >= 1; i--)
        for(int j = 1; j <= N; j++)
            if(NotNull(sys[i][j]))
            {
                ans[j] = sys[i][N + 1];

                for(int c = j + 1; c <= N; c++)
                    ans[j] -= sys[i][c] * ans[c];

                break;
            }

    fout << fixed << setprecision(10) << ans[1] << '\n';

    return 0;
}