#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;
}