#include <bits/stdc++.h>

#define EPS 0.0001
using namespace std;

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

const int NMAX(260);
double mat[NMAX][NMAX], sol[NMAX];
int n, m;
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 l = i + 1; l <= n; ++l)
        {
            for(int c = j + 1; c <= n + 1; ++c)
                mat[l][c] -= mat[l][j] * mat[i][c];
            mat[l][j] = 0;
        }
        ++i, ++j;
    }
    for(i = n; i >= 1; --i)
        for(int j = 1; j <= n + 1; ++j)
            if(mat[i][j] > EPS || mat[i][j] < -EPS)
            {
                if(j == n + 1){
                    sol[0] = -1;
                    break;
                }

                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){
        int a, b, c;
        fin >> a >> b >> c;
        mat[a][n + 1] -= c;
        mat[a][b]++;
        mat[a][a]--;
        mat[b][n + 1] -= c;
        mat[b][a]++;
        mat[b][b]--;
    }

    Gauss();

    fout << fixed << setprecision(4) << sol[1] << '\n';
    return 0;
}