#include<cstdio>

#include<stack>

#include<vector>

#include<iostream>

using namespace std;

const int N = 100005;

#define debug(a) cout<<#a<<"="<<a<<" "

#define ct cout<<endl

#define _ct cout<<"----------"<<endl

int n,m,cnt,bcnt;

int dfsn[N],low[N],ins[N],b[N],sz[N],vis[N];

vector<int> g[N];

vector<int> h[N];

int du[N];

stack<int> stk;

inline int in(int x=0,char ch=getchar()){ while(ch>'9'||ch<'0') ch=getchar();

	while(ch>='0'&&ch<='9') x=(x<<3)+(x<<1)+ch-'0',ch=getchar();return x; }

void Tarjan(int u){

	dfsn[u]=low[u]=++cnt,ins[u]=1,stk.push(u);

	for(int i=0,lim=g[u].size(),v;i<lim;i++){

		v=g[u][i];

		if(!dfsn[v]){ Tarjan(v),low[u]=min(low[u],low[v]); }

		else if(ins[v]) low[u]=min(low[u],dfsn[v]);

	}if(dfsn[u]==low[u]){

		++bcnt;int v=-1;

		for(;u!=v;){ v=stk.top(),stk.pop(),ins[v]=0,b[v]=bcnt,sz[bcnt]++; }

	}

}

int check(int x){

	for(int i=0,lim=h[x].size();i<lim;i++) if(du[h[x][i]]<=1) return 0;

	return 1;

}

int main(){

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

	n=in(),m=in();

	for(int i=1,u,v;i<=m;i++) u=in(),v=in(),g[u].push_back(v);

	for(int i=1;i<=n;i++) if(!dfsn[i]) Tarjan(i);

//	_ct;debug(bcnt),ct;

	for(int i=1;i<=n;i++){

		for(int j=0,lim=g[i].size();j<lim;j++) if(b[i]!=b[g[i][j]]&&!vis[b[g[i][j]]])

			vis[b[g[i][j]]]=1,h[b[i]].push_back(b[g[i][j]]),du[b[g[i][j]]]++;

		for(int j=0,lim=g[i].size();j<lim;j++) if(b[i]!=b[g[i][j]]) vis[b[g[i][j]]]=0;

	}

//	_ct;

	int ans=0;

	for(int i=1;i<=bcnt;i++) if(du[i]==0) ans++;

	for(int i=1;i<=bcnt;i++) if(du[i]==0&&sz[i]==1&&check(i)){ ans--;break; }

//	debug(ans),ct;

	printf("%.6lf\n",(double)(n-ans)/n);

	return 0;

}