#include <vector>
#include <fstream>
#include <cmath>
#include <cstring>
#include <iomanip>
using namespace std;
const double eps=0.0000000001;
const int NMAX=260;
int n, i, x, y, c, k;
double sol[NMAX], a[NMAX][NMAX];
vector< pair<int,int> > g[NMAX];
void gauss()
{
    int i=1, j=1, l, p;
    while(i<=n&&j<=n)
    {
        for(k=i; k<=n; k++)
            if(a[k][j]<-eps||a[k][j]>eps) break;
        if(k==n+1)
        {
            j++;
            continue;
        }

        if(k!=i)
            for(l=1; l<=n+1; l++)
                swap(a[i][l],a[k][l]);

        for(l=j+1; l<=n+1; l++)
            a[i][l]/=a[i][j];

        a[i][j]=1.00;

        for(p=i+1; p<=n; p++)
        {
            for(l=j+1; l<=n+1; l++)
                a[p][l]-=a[i][l]*a[p][j];
            a[p][j]=0;
        }

        i++;
        j++;
    }
    for(i=n; i>=1; i--)
        for(j=1; j<=n; j++)
        {
            if(a[i][j]>-eps&&a[i][j]<eps) continue;
            sol[j]=a[i][n+1];
            for(l=j+1; l<=n; l++)
                sol[j]-=a[i][l]*sol[l];
            break;
        }
}
int main()
{
    ifstream in("tunel.in");
    ofstream out("tunel.out");
    in>>n>>k;
    for(i=1; i<=k; i++)
    {
        in>>x>>y>>c;
        g[x].push_back(make_pair(y,c));
        g[y].push_back(make_pair(x,c));
    }
    for(i=1; i<n; i++)
    {
        a[i][i]=1;
        double coef=1.00/g[i].size();
        for(vector< pair<int,int> >::iterator it=g[i].begin(); it!=g[i].end(); it++)
        {
            a[i][it->first]-=coef;
            a[i][n+1]+=coef*it->second;
        }
    }
    a[n][n]=1;
    gauss();
    out<<setprecision(4)<<sol[1]<<'\n';
    return 0;
}