#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;

const int N = 260;

int n;

double r[N], g[N][N];

vector <pair <int, int> > L[N];

void read() {
  int m, x, y, c;

  scanf("%d%d", &n, &m);
  
  for (int i = 1; i <= m; ++ i) {
    scanf("%d%d%d", &x, &y, &c);
    
    L[x].push_back(make_pair(y, c));
    L[y].push_back(make_pair(x, c));
  }
}

void init_gauss() {
  for (int i = 1; i < n; ++ i) {
    g[i][i] = 1;

    double c = (double)1 / L[i].size();

    for (int j = 0; j < L[i].size(); ++ j) {
      g[i][L[i][j].first] = - c;
      r[i] += c * L[i][j].second;
    }
  }
  
  g[n][n] = 1;
  r[n] = 0;
}

void gauss() {
  for (int j = 1; j <= n; ++ j) {
    int i = 0;
    
    for (i = j; i <= n; ++ i)
      if (g[i][j])
        break;
  
    if (i != j) {
      swap(g[i], g[j]);
      swap(r[i], r[j]);
    }

    for (i = 1; i <= n; ++ i)
      if (i != j) {
        double deinm = - g[i][j] / g[j][j];

        for (int k = 1; k <= n; ++ k)
          g[i][k] += deinm * g[j][k];

        r[i] += deinm * r[j];
      }
  }

  printf("%.4lf\n", r[1] / g[1][1]);
}



int main() {
  freopen("tunel.in", "r", stdin);
  freopen("tunel.out", "w", stdout);

  read();
  init_gauss();
  gauss();

  return 0;
}