#include <bits/stdc++.h>

#define Nmax 257
#define EPS 1e-6

using namespace std;

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

int N, M;
int G[Nmax][Nmax];
int deg[Nmax];
double ans[Nmax], D[Nmax], S[Nmax][Nmax];
int F[Nmax][Nmax];

int main()
{
    fin >> N >> M;
    while(M--)
    {
        int x, y, c;
        fin >> x >> y >> c;
        deg[x]++;
        deg[y]++;
        G[x][y] += c;
        G[y][x] += c;
        F[x][y]++;
        F[y][x]++;
    }
    for(int i = 1; i <= N; i++)
    {
        for(int j = 1; j <= N; j++)
        {
            if(F[i][j])
                S[i][j] = (double)-F[i][j] / deg[i];
            ans[i] += G[i][j];
        }
        ans[i] /= deg[i];
        S[i][i] = 1;
    }
    for(int i = 1; i < N; i++)
        for(int j = i + 1; j < N; j++)
            if(S[i][i] != 0)
            {
                double q = S[j][i] / S[i][i];
                for(int k = 1; k < N; k++)
                {
                    S[j][k] -= q * S[i][k];
                    if(abs(S[j][k]) < EPS)
                       S[j][k] = 0;
                }
                ans[j] -= q * ans[i];
                if(abs(ans[j]) < EPS)
                    ans[j] = 0;
            }

    for(int i = N - 1; i >= 1; i--)
    {
        D[i] = ans[i];
        for(int j = i + 1; j < N; j++)
            D[i] = D[i] - S[i][j] * D[j];
        if(D[i] != 0)
            D[i] = D[i] / S[i][i];
    }
    fout << fixed << setprecision(7) << D[1] << "\n";
    return 0;
}