#include<stdio.h>
#include<vector>
#include<algorithm>

using namespace std;

#define NMAX 256

#define mp make_pair
#define f first
#define s second

int n, m;
double a[NMAX][NMAX], b[NMAX];

vector<pair<int, int> > v[NMAX];

void Gauss()
{
    double pb;

    for(int i, j=1; j<=n; ++j)
    {
        for(i=j; i<=n; ++i)
            if(a[i][j])
                break;

        for(int k=1; k<=n; ++k)
            swap(a[i][k], a[j][k]);
        swap(b[i], b[j]);

        for(i=1; i<=n; ++i)
        {
            if(i==j)
                continue;

            pb=a[i][j]/a[j][j];

            for(int k=1; k<=n; ++k)
                a[i][k]-=pb*a[j][k];
            b[i]-=pb*b[j];
        }
    }

    printf("%lf\n", b[1]/a[1][1]);
}

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

    int x, y, c;
    double pb;

    scanf("%d%d", &n, &m);

    for(int i=1; i<=m; ++i)
    {
        scanf("%d%d%d", &x, &y, &c);

        v[x].push_back(mp(y, c));
        v[y].push_back(mp(x, c));
    }

    for(int i=1; i<n; ++i)
    {
        a[i][i]=1;

        pb=(double)1/v[i].size();

        for(int j=0; j<v[i].size(); ++j)
        {
            a[i][v[i][j].f]-=pb;

            b[i]+=pb*v[i][j].s;
        }
    }
    a[n][n]=1;

    Gauss();

    return 0;
}