#include <algorithm>
#include <vector>
using namespace std;

#define pb push_back
#define mp make_pair
#define sc second
#define fs first
#define DIM 260

vector <pair <int,int> > g[DIM];
double bst[DIM][DIM];
int grd[DIM];
int n,m;

void read ()
{
    int i,x,y,z;

    scanf ("%d%d",&n,&m);
    for (i=1; i<=m; ++i)
    {
        scanf ("%d%d%d",&x,&y,&z);
        ++grd[x]; ++grd[y];
        g[x].pb (mp (y,z));
        g[y].pb (mp (x,z));
    }
}

void solve ()
{
    vector <pair <int,int> > :: iterator it;
    double nr1,nr2;
    int i,j,k;

    for (i=1; i<n; ++i)
        for (it=g[i].begin (); it!=g[i].end (); ++it)
        {
            bst[i][it->fs]+=(double)1/grd[i];
            bst[i][0]+=(double)it->sc/grd[i];
        }
    for (i=2; i<n; ++i)
    {
        nr1=1-bst[i][i];
        for (j=0; j<n; ++j)
            bst[i][j]*=(double)1/nr1;
        bst[i][i]=0;
        for (j=1; j<n; ++j)
        {
            nr2=bst[j][i];
            for (k=0; k<n; ++k)
                bst[j][k]+=bst[i][k]*nr2;
            bst[j][i]=0;
        }
    }
    printf ("%lf",bst[1][0]/(1-bst[1][1]));
}

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

    read ();
    solve ();

    return 0;
}