#include <bits/stdc++.h>
#define int long long
#define double long double
using namespace std;

ifstream in("ciclu.in");
ofstream out("ciclu.out");

vector <pair <int, int>>  g[1105];

int n, m;

int dp[1105][1105];

double medie[1105];

signed main()
{
    in >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y, w;
        in >> x >> y >> w;
        x--;
        y--;
        g[x].push_back({y, w});
    }

    ///

    for(int i = 0; i <= n; i++)
    {
        for(int j = 0; j < n; j++)
        {
            dp[i][j] = -1;
        }
    }
    dp[0][0] = 0;

    for(int k = 1; k <= n; k++)
    {
        for(int vertex = 0; vertex < n; vertex++)
        {
            for(auto it:g[vertex])
            {
                if(dp[k - 1][it.first] == -1)
                    continue;
                int gr = it.second;
                if(dp[k][vertex] == -1)
                    dp[k][vertex] = dp[k - 1][it.first] + gr;
                else
                    dp[k][vertex] = min(dp[k][vertex], dp[k - 1][it.first] + gr);
            }
        }
    }

    ///

    for(int i = 0; i < n; i++)
    {
        if(dp[n][i] == -1)
            continue;
        for(int k = 0; k < n; k++)
        {
            if(dp[k][i] != -1)
                medie[i] = max(medie[i],((double)dp[n][i] - dp[k][i]) / (n - k));
        }
    }

    ///

    double rasp = medie[0];
    for(int i = 0; i < n; i++)
    {
        if(medie[i] > 0)
            rasp = min(rasp, medie[i]);
    }
    out << fixed << setprecision(2) << rasp;
    return 0;
}