#include<bits/stdc++.h>
using namespace std;
#define endl "\n"
#define int long long 
const int MAXN=100000;
const int INF=0x1f1f1f1f1f1f1f1f;
int n,m;
vector<pair<int,int> > e[MAXN+5];
double dp[MAXN+5];
double dfs(int u,int fa)
{
	if(u==n||dp[u])
		return dp[u];
	double res=0;
	int k=e[u].size();
	for(int i=0;i<e[u].size();i++)
	{
		int v=e[u][i].first;
		int w=e[u][i].second;
		if(v==fa)
			continue;
		res+=(dfs(v,u)+w)/k;
	}
	return dp[u]=res;
}
signed main()
{
//	ios::sync_with_stdio(false);
//	cin.tie(0);
	cin>>n>>m;
	for(int i=1;i<=m;i++)
	{
		int u,v,w;
		cin>>u>>v>>w;
		e[u].push_back(make_pair(v,w));
	}
	cout<<fixed<<setprecision(2)<<dfs(1,-1)<<endl;
	return 0;
}