#include <fstream>
#include <iomanip>
#define nmax 260
using namespace std;
ifstream f("tunel.in");
ofstream g("tunel.out");
double c[nmax][nmax],a[nmax];
int n,m;

int main()
{
    int i,j,k,x,y,z;
    f>>n>>m;n--;
    for (i=1;i<=m;i++) {
        f>>x>>y>>z;
        c[x][y]++;
        a[x]++;
        c[y][x]++;
        a[y]++;

        c[x][0]+=1.0*z;
        c[y][0]+=1.0*z;
    }
    for (i=1;i<=n;i++)
        for (j=0;j<=n;j++)
            c[i][j]/=a[i];

    for (i=2;i<=n;i++)
        for (j=1;j<=n;j++)
            for (k=0;k<=n;k++)
                    if(j!=i&&k!=i)
                        c[j][k]+=c[i][k]*1.0/(1-c[i][i])*c[j][i];

    g<<setprecision(6)<<fixed<<(1.0/(1.0-c[1][1]))*c[1][0];

}