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

using namespace std;

int n, m, cost[MAXN][MAXN];
double ec[MAXN][MAXN], sol[MAXN];

void update(int a, int b, int c)
{
    ec[a][a]++;
    ec[a][b]--;
    ec[a][n+1] += c;
}

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);
        if (a != n)
            update(a, b, c);
        if (b != n)
            update(b, a, c);
    }
    ec[n][n] = 1;
}

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

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

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

    return 0;
}