#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
#include<vector>
#include<queue>
using namespace std;
#define MAXN 100001
#define MAXM 300001
struct people
{
	int to,next,from;
};
people a[MAXM];
int N,M,last[MAXN],step=0,tot1=0,tot=0,LOW[MAXN],DFN[MAXN],stack[MAXN],ans=0;
int belong[MAXN],indegree[MAXN],IN,OUT,ans1=0,size1[MAXN],ans2=0;
bool instack[MAXN];
void add(int x,int y)
{
	a[++tot].to=y;
	a[tot].from=x;
	a[tot].next=last[x];
	last[x]=tot;
}
void Tarjan(int now)
{
	DFN[now]=LOW[now]=++step;
	stack[++tot1]=now;
	instack[now]=true;
	for(int i=last[now]; i; i=a[i].next)
	{
		int now_to=a[i].to;
		if(!DFN[now_to])
		{
			Tarjan(now_to);
			LOW[now]=min(LOW[now_to],LOW[now]);
		}
		else if(instack[now_to])
			LOW[now]=min(DFN[now_to],LOW[now]);
	}

	if(DFN[now]==LOW[now])
	{
		int now_out;
		ans++;
		do
		{
			now_out=stack[tot1--];
			instack[now_out]=false;
			belong[now_out]=ans;
			size1[ans]++;
		}
		while(now_out!=now);
	}
}
int main()
{
//	freopen("input.in","r",stdin);
//	freopen("output.out","w",stdout);
	memset(belong,0,sizeof(belong));
	memset(DFN,0,sizeof(DFN));
	memset(LOW,0,sizeof(LOW));
	memset(last,0,sizeof(last));
	memset(instack,false,sizeof(instack));
	scanf("%d%d",&N,&M);
	for(int i=1; i<=M; i++)
	{
		int A,B;
		scanf("%d%d",&A,&B);
		add(A,B);
	}
	for(int i=1; i<=N; i++)
		if(!DFN[i])
			Tarjan(i);
	for(int i=1; i<=tot; i++)
	{
		if(belong[a[i].to]!=belong[a[i].from])
			indegree[belong[a[i].to]]++;
	}

	for(int i=1; i<=ans; i++)
		if(!indegree[i])
			ans1++;
	if(ans1>1)
		for(int i=1; i<=ans; i++)
			if(!indegree[i] && size1[i]==1)
			{
				ans1--;
				break;
			}
	printf("%.6lf\n",1-(double)ans1/N);
	//system("pause");
	return 0;
}