#include<fstream>
#include<vector>
#include<cmath>
#include<iomanip>
#define pb push_back
using namespace std;
const double ep=1e-6;
double a[300][300],p;
vector <int> b[300],c[300];
int i,n,m,j,k,x,y,z;
void sw(int x,int y)
{
    int i;
    for (i=1;i<=n;i++)
        swap(a[x][i],a[y][i]);
}
int main()
{
    ifstream f("tunel.in");
    ofstream g("tunel.out");
    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y>>z;
        b[x].pb(y);
        b[y].pb(x);
        c[x].pb(z);
        c[y].pb(z);
    }
    a[n][n]=1;
    for (i=1;i<n;i++)
    {
        a[i][i]=b[i].size();
        for (j=0;j<b[i].size();j++)
        {
            a[i][b[i][j]]-=1;
            a[i][n+1]+=c[i][j];
        }
    }
    for (i=1;i<=n;i++)
    {
        if (fabs(a[i][i])<ep)
            for (j=i+1;j<=n;j++)
                if (fabs(a[j][i])>ep)
                {
                    sw(i,j);
                    break;
                }
        for (j=1;j<=n;j++)
            if (i!=j)
            {
                p=a[j][i]/a[i][i];
                for (k=1;k<=n+1;k++)
                    a[j][k]-=a[i][k]*p;
            }
    }
    g<<setprecision(6)<<fixed<<a[1][n+1]/a[1][1];
    return 0;
}