#include <bits/stdc++.h>

#define setIO(s) freopen(s".in","r",stdin)

#define maxn 200003

using namespace std;

queue <int> Q;

int n, m, edges;

int hd[maxn], to[maxn], nex[maxn], deg[maxn], done[maxn];

double val[maxn], f[maxn], k[maxn];

void add(int u, int v, double c)

{

    nex[++edges] = hd[u], hd[u] = edges, to[edges] = v, val[edges] = c;

}

int main()

{

    // setIO("input");

    scanf("%d%d",&n,&m);

    for(int i = 1; i <= m; ++i)

    {

        int a, b;

        double c;

        scanf("%d%d%lf",&a,&b,&c), add(b, a, 1.0*c), ++deg[a], ++k[a];

    }

    Q.push(n);

    while(!Q.empty())

    {

        int u = Q.front(); Q.pop();

        for(int i = hd[u]; i ; i = nex[i])

        {

            int v = to[i];

            deg[v]--;

            f[v] += (f[u] + val[i]) / (1.0 * k[v]);

            if(!deg[v])

                Q.push(v);

        }

    }

    printf("%.2f",f[1]);

    return 0;

}