#include<bits/stdc++.h>

using namespace std;

#define MAXN 200010
#define MAXM 2000010
int Dfn[MAXN];
int Low[MAXN];
int Stack[MAXN];
int Top = 0;
int Point[MAXN];
bool Ins[MAXN];
int Index;
int Head[MAXN];
int End[MAXM];
int Next[MAXM];
int Head2[MAXN];
int End2[MAXM];
int Next2[MAXM];
bool Used[MAXN];
int Dis[MAXN];
int Degree[MAXN];
int Cnt = 0;
int Cou_p[MAXN]; 

void Tarjan(int Cur){ // 以烈焰净化一切的环！（大雾） 
	Dfn[Cur] = Low[Cur] = ++Index;
	Ins[Cur] = true;
	Stack[++Top] = Cur; 
	for(int x = Head[Cur]; x != -1; x = Next[x]){
		if(Dfn[End[x]] == -1){
			Tarjan(End[x]);
			if(Low[End[x]] < Low[Cur])
				Low[Cur] = Low[End[x]];
		}
		else if(Ins[End[x]] && Dfn[End[x]] < Low[Cur])
			Low[Cur] = Dfn[End[x]];
	}
	if(Dfn[Cur] == Low[Cur]){
		Cnt++;
		do{
			Cou_p[Cnt]++;
			Point[Stack[Top]] = Cnt;
			Ins[Stack[Top]] = false;
		}while(Stack[Top--] != Cur);
	}
}

int Cou = 0;
void Link(int a, int b){ // 连边 
	Next[++Cou] = Head[a];
	Head[a] = Cou;
	End[Cou] = b;
}
int Cou2 = 0;
void Relink(int a, int b){ // 重连边 
	Next2[++Cou2] = Head2[a];
	Head2[a] = Cou2;
	End2[Cou2] = b;
}

bool Single(int xx){
	for(int x = Head2[xx]; x != -1; x = Next2[x])
		if(Degree[End2[x]] == 1)
			return false;
	return true;
}
int main(){
	memset(Head, -1, sizeof(Head));
	memset(Head2, -1, sizeof(Head2));
	memset(Dfn, -1, sizeof(Dfn));
	int n, m;
	scanf("%d %d", &n, &m);
	for(int i = 1; i <= m; i++){
		int a, b;
		scanf("%d %d", &a, &b);
		Link(a, b);
	}
	for(int i = 1; i <= n; i++)
		if(Dfn[i] == -1)
			Tarjan(i);
	for(int i = 1; i <= n; i++) // 重建图 
		for(int x = Head[i]; x != -1; x = Next[x])
			if(Point[i] != Point[End[x]]){
				Relink(Point[i], Point[End[x]]);
				Degree[Point[End[x]]]++;
			}
	int Ans = 0;
	bool Have_one = false;
	for(int i = 1; i <= Cnt; i++){
		if(!Have_one && Cou_p[i] == 1 && Degree[i] == 0 && Single(i)) // 是否可以使用“排除法” 
			Have_one = true;
		if(Degree[i] == 0)
			Ans++; 
	}
	if(Have_one) Ans--;
	printf("%.6lf", 1.0 - (double)Ans / (double)n);
}