#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

const double eps=0.00000001;

struct edge
{
    int nod,cost;
};

vector<edge> v[260];
int n,m;
double v1[260][260];
double sol[260];

void gauss()
{
    int i=1,j=1;
    while(i<n && j<=n)
    {
        int k;
        for(k=i;k<n && abs(v1[k][j])<eps;k++);
        if(k>=n) {j++;continue;}
        swap(v1[i],v1[k]);
        for(int k=i+1;k<n;k++)
        {
            double p=v1[k][j]/v1[i][j];
            for(int q=j;q<=n+1;q++) v1[k][q]-=p*v1[i][q];
            v1[k][j]=0;
        }
        i++;j++;
    }
    for(int i=n-1;i>=1;i--)
        for(int j=1;j<=n+1;j++)
            if(abs(v1[i][j])>eps)
            {
                sol[j]=v1[i][n+1];
                for(int k=j+1;k<=n;k++) sol[j]-=v1[i][k]*sol[k];
                sol[j]/=v1[i][j];
                break;
            }
}

int main()
{
    freopen("tunel.in","r",stdin);
    freopen("tunel.out","w",stdout);
    int x,y,c;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d%d",&x,&y,&c);
        v[x].push_back({y,c});
        v[y].push_back({x,c});
    }
    for(int i=1;i<n;i++)
    {
        int k=v[i].size();
        v1[i][i]=1;
        for(int j=0;j<v[i].size();j++)
        {
            int nod=v[i][j].nod,dist=v[i][j].cost;
            v1[i][nod]-=(1.0)/k;
            v1[i][n+1]+=(1.0*dist)/k;
        }
    }
    gauss();
    printf("%.6f",sol[1]);
    return 0;
}