#include <cstdio>
#include <cmath>
#include <algorithm>
 
using namespace std;
 
#define Nmax 256
#define Mmax 100015
 
const double eps = 10e-8;
 
int n, m;
int x[Mmax], y[Mmax], cost[Mmax];
int gr[Nmax];
double a[Nmax][Nmax], b[Nmax];
 
void citire()
{
    int i;
 
    scanf("%d %d\n", &n, &m);
    for (i = 1; i <= m; ++i)
    {
        scanf("%d %d %d\n", &x[i], &y[i], &cost[i]);
        ++gr[x[i]], ++gr[y[i]];
    }
}
 
int is0(double a)
{
    return (fabs(a) < eps);
}
 
void gauss()
{
    int i, j, k;
    double d;
 
    for (i = 1; i <= n; ++i)
    {
        if (is0(a[i][i]))
        {
            for (j = i; j <= n; ++j)
                if (!is0(a[j][i]))
                    break;
 
            for (k = i; k <= n; ++k)
                swap(a[i][k], a[j][k]);
            swap(b[i], b[j]);
        }
 
        d = a[i][i];
 
        for (j = i; j <= n; ++j)
            a[i][j] /= d;
        b[i] /= d;
 
        for (j = 1; j <= n; ++j)
            if (i != j && !is0(a[j][i]))
            {
                d = a[j][i];
                for (k = i; k <= n; ++k)
                    a[j][k] -= a[i][k] * d;
                b[j] -= b[i] * d;
            }
    }
}
 
void solve()
{
    int i;
 
    for (i = 1; i <= n; ++i)
    {
        a[x[i]][x[i]] = -1;
        a[y[i]][y[i]] = -1;
    }
 
    for (i = 1; i <= m; ++i)
    {
        b[x[i]] -= (double)cost[i] / gr[x[i]];
        a[x[i]][y[i]] += 1.0 / gr[x[i]];
 
        b[y[i]] -= (double)cost[i] / gr[y[i]];
        a[y[i]][x[i]] += 1.0/ gr[y[i]];
    }
 
    --n;
 
    gauss();
 
    printf("%lf\n", b[1]);
}
 
int main()
{
    freopen("tunel.in", "r", stdin);
    freopen("tunel.out", "w", stdout);
 
    citire();
    solve();
 
    return 0;
}