#include <iostream>
#include <cstdio>
#include <vector>
#define MAXN 265

using namespace std;

vector<int> graf[MAXN];
int n, m, cost[MAXN][MAXN];
double ec[MAXN][MAXN], sol[MAXN];

void read()
{
    int a, b, c;
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= m; i++) {
        scanf("%d %d %d", &a, &b, &c);
        graf[a].push_back(b);
        graf[b].push_back(a);
        cost[a][b] = cost[b][a] = c;
    }
}

void buildEc()
{
    for (int i = 1; i < n; i++) {
        ec[i][i] = graf[i].size();
        for (int y : graf[i]) {
            ec[i][y]--;
            ec[i][n+1] += cost[i][y];
        }
    }
    ec[n][n] = 1;
}

/// GAUSS
double solveEc()
{
    for (int i = 1; i < n; i++) {
        double x = ec[i][i];
        for (int j = i+1; j <= n; j++) {
            if (ec[j][i] != 0) {
                double fact = x / ec[j][i];
                for (int k = i; k <= n+1; k++)
                    ec[j][k] = fact * ec[j][k] - ec[i][k];
            }
        }
    }
    for (int i = n; i >= 1; i--) {
        sol[i] = ec[i][n+1];
        for (int j = i+1; j <= n; j++)
            sol[i] -= sol[j] * ec[i][j];
        sol[i] /= ec[i][i];
    }
    return sol[1];
}

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

    read();
    buildEc();
    double rez = solveEc();
    printf("%f", rez);

    return 0;
}