#include <map>

#include <cmath>

#include <queue>

#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

using namespace std;

#define F(i,j,k) for (int i=j;i<=k;++i)

#define D(i,j,k) for (int i=j;i>=k;--i)

#define ll long long

#define mp make_pair

#define maxn 600005

struct Graph{

    int n,fr[maxn],h[maxn],to[maxn],ne[maxn],en,inside[maxn];

    int sta[maxn],top,bel[maxn],idx,vcnt,siz[maxn];

    int dfn[maxn],low[maxn],ins[maxn],in[maxn],out[maxn];

    void init(){memset(h,-1,sizeof h); en=0;idx=0;vcnt=0;}

    void add(int a,int b)

    {fr[en]=a;to[en]=b;ne[en]=h[a];h[a]=en++;out[a]++;in[b]++;}

    void Tarjan(int o)

    {

        low[o]=dfn[o]=++idx;ins[o]=1;

        sta[++top]=o;

        for (int i=h[o];i>=0;i=ne[i])

            if (!low[to[i]]) Tarjan(to[i]),low[o]=min(low[o],low[to[i]]);

            else if (ins[to[i]]) low[o]=min(low[o],dfn[to[i]]);

        if (low[o]==dfn[o])

        {

            int x=-1; vcnt++;

            while (x!=o)

            {

                x=sta[top--];

                bel[x]=vcnt;

                siz[vcnt]++;

                ins[x]=0;

            }

        }

    }

    void Solve(){F(i,1,n)if(!dfn[i])Tarjan(i);}

    int cal()

    {

        int ret=0;

        F(i,1,n) if (!in[i]) ret++;

        return ret;

    }

    int flag()

    {

//      memset(vis,0,sizeof vis);

        int ret=0;

        F(i,1,n)

        {

            if (siz[bel[i]]==1&&in[i]==0)

            {

                int tmp=0x3f3f3f3f,flag=0;

                for (int j=h[i];j>=0;j=ne[j])

                {

                    flag=1;

                    tmp=min(inside[bel[to[j]]],tmp);

                }

                if ((tmp>=2&&flag)||in[i]+out[i]==0) ret=1;

            }

        }

        return ret;

    }

}G1,G2;

int n,m;

int vis[maxn];

int main()

{

//  freopen("killer1.in","r",stdin);

    scanf("%d%d",&n,&m);G1.init();G2.init();

//  if (n==1){printf("0.000000\n");return 0;}

    F(i,1,m){int u,v;scanf("%d%d",&u,&v);G1.add(u,v);}

    G1.n=n;G1.Solve();

    F(i,1,n)

        for (int j=G1.h[i];j>=0;j=G1.ne[j]){

            if (G1.bel[G1.fr[j]]!=G1.bel[G1.to[j]]&&vis[G1.to[j]]!=i)

            {

                vis[G1.to[j]]=i;

                G2.add(G1.bel[G1.fr[j]],G1.bel[G1.to[j]]);

                G1.inside[G1.bel[G1.to[j]]]++;

            }

        }

    G2.n=G1.vcnt;

    printf("%.6f\n",1.0*(n-G2.cal()+G1.flag())/(n*1.0));

}