#include <bits/stdc++.h>

using namespace std;

const float eps = 1e-6;
const int MAXN = 255;

vector < pair <int, int> > g[MAXN + 1];

float eqs[MAXN + 1][MAXN + 2];
float dp[MAXN + 1];

int main() {
    FILE *fi, *fout;
    int i, n, m, j;
    fi = fopen("tunel.in" ,"r");
    fout = fopen("tunel.out" ,"w");
    fscanf(fi,"%d %d " ,&n,&m);
    for(i = 1; i <= m; i++) {
        int a, b, c;
        fscanf(fi,"%d %d %d " ,&a,&b,&c);
        g[a].push_back({b, c});
        g[b].push_back({a, c});
    }
    // dp[nod] = suma((1 / deg[nod]) * (dp[it.first] + it.second));
    // dp[n] = 0;
    for(int nod = 1; nod < n; nod++) {
        int deg = g[nod].size();
        for(auto it : g[nod]) {
            eqs[nod][it.first] += 1.0;
            eqs[nod][n + 1] -= 1.0 * it.second;
        }
        eqs[nod][nod] -= 1.0 * deg;
    }
    for(int nod = 1; nod < n; nod++) {
        eqs[nod][n] = 0.0;
    }
    int l = 1, c = 1;
    while(l < n && c <= n) {
        i = l;
        while(i <= n && fabs(eqs[i][c]) < eps) {
            i++;
        }
        if(i == n + 1) {
            c++;
        }
        else {
            for(j = c; j <= n + 1; j++) {
                swap(eqs[l][j], eqs[i][j]);
            }
            for(j = n + 1; j >= c; j--) {
                eqs[l][j] /= eqs[l][c];
            }
            for(i = l + 1; i < n; i++) {
                for(j = n + 1; j >= c; j--) {
                    eqs[i][j] -= eqs[l][j] * eqs[i][c];
                }
            }
            l++;
            c++;
        }
    }
    for(i = n - 1; i >= 1; i--) {
        j = 1;
        while(j <= n && fabs(eqs[i][j]) < eps) {
            j++;
        }
        dp[i] = eqs[i][n + 1];
        for(int p = j + 1; p <= n; p++) {
            dp[i] -= dp[p] * eqs[i][p];
        }
    }
    fprintf(fout,"%.6f" ,dp[1]);
    fclose(fi);
    fclose(fout);
    return 0;
}