#include <fstream>
#include <vector>
using namespace std;
ifstream in("tunel.in");
ofstream out("tunel.out");
double ep,a[305][305],z,ras;
int n,m,x,y,i,j,k,t,ma[305][305];
vector <pair<int,double> > v[305];
int ze(double a)
{
    if (a>ep||a<-ep) return 1;
    return 0;
}
int main()
{
    in>>n>>m;
    ep=0.00000001;
    for(i=1;i<=m;++i)
    {
        in>>x>>y>>z;
        v[x].push_back({y,z});
        v[y].push_back({x,z});
        ma[x][y]++;
        ma[y][x]++;
    }
    a[1][n]=-1;
    for (i=1;i<=n-1;++i)
        for (j=1;j<=n-1;++j)
    {
        if (i==j) {a[i][j]=-1;}
        else {a[i][j]=double(ma[i][j])/double(v[j].size());}
    }
    i=j=1;
    while (i<n&&j<n)
    {
        for (k=i;k<n;++k)
            if (ze(a[k][j])) break;
        for (t=1;t<=n;++t)
            swap(a[i][t],a[k][t]);
        for (k=j+1;k<=n;++k)
            a[i][k]/=a[i][j];
        a[i][j]=1;
        for (k=1;k<n;++k)
            if (k!=i)
        {for (t=j+1;t<=n;++t)
            {a[k][t]-=a[k][j]*a[i][t]; a[k][t]*=ze(a[k][t]);}
            a[k][j]=0;
        }
        i++; j++;
    }
    for (i=1;i<n;++i)
        for (j=0;j<v[i].size();++j)
    {
        ras=ras+a[i][n]*v[i][j].second/double(v[i].size());
    }
    out<<ras;
    return 0;
}
///val[i]=