#include <bits/stdc++.h>
using namespace std;
const int N=1e5+10;
vector<int>G1[N], G2[N]; 
int tsp, cnt, dfn[N], low[N], scc[N], num[N];
stack<int> stk;bool instk[N];
void tarjan(int x)
{
	dfn[x]=low[x]=++tsp;
	stk.push(x);instk[x]=1;
	for(int y:G1[x])
	{
		if(!dfn[y])
		{
			tarjan(y);
			low[x]=min(low[x], low[y]);
		}
		else if(instk[y])low[x]=min(low[x], dfn[y]);
	}
	if(dfn[x]==low[x])
	{
		cnt++;
		for(int z=-1;z!=x;)
		{
			z=stk.top();stk.pop();instk[z]=0;
			scc[z]=cnt;
			num[cnt]++;
		}
	}
}

int main()
{
	int n, m;scanf("%d%d", &n, &m);
	for(int i=1, x, y; i <= m; i++)
	{
		scanf("%d%d", &x, &y);
		G1[x].push_back(y);
	}

	tsp=cnt=0;memset(dfn, 0, sizeof(dfn));memset(low, 0, sizeof(low));
    memset(instk, 0, sizeof(instk));
	memset(scc, 0, sizeof(scc));
	memset(num, 0, sizeof(num));
	for(int i=1;i <= n;i++)if(dfn[i]==0)tarjan(i);
	
    map<pair<int, int>, bool>mp; vector<int>rd(cnt+1);
	for(int i=1;i <= n;i++)for(int j:G1[i])
    {
        int x=scc[i], y=scc[j];
        if(x!=y && !mp[{x, y}])G2[x].push_back(y), rd[y]++, mp[{x, y}]=1;
    }
		
	int p=0;for(int i=1;i <= cnt;i++)if(!rd[i])p++;
	
	for(int i=1;i <= cnt;i++)if(num[i]==1 && rd[i]==0)
	{
		bool flag=0;
		for(int j:G2[i])if(rd[j]==1){flag=1;break;}
		if(!flag){p--;break;}
	}
	printf("%.6lf\n", 1.0 - 1.0*p/n );	
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+10;
vector<int>G1[N],G2[N]; 
int tsp,cnt,dfn[N],low[N],scc[N],num[N];
stack<int> stk;bool instk[N];
void tarjan(int x)
{
	dfn[x]=low[x]=++tsp;
	stk.push(x);instk[x]=1;
	for(int y:G1[x])
	{
		if(!dfn[y])
		{
			tarjan(y);
			low[x]=min(low[x],low[y]);
		}
		else if(instk[y])low[x]=min(low[x],dfn[y]);
	}
	if(dfn[x]==low[x])
	{
		cnt++;
		for(int z=-1;z!=x;)
		{
			z=stk.top();stk.pop();instk[z]=0;
			scc[z]=cnt;
			num[cnt]++;
		}
	}
}

int main()
{
	int n,m;scanf("%d%d",&n,&m);
	for(int i=1,x,y;i<=m;i++)
	{
		scanf("%d%d",&x,&y);
		G1[x].push_back(y);
	}

	tsp=cnt=0;memset(dfn,0,sizeof(dfn));memset(low,0,sizeof(low));
    memset(instk,0,sizeof(instk));
	memset(scc,0,sizeof(scc));
	memset(num,0,sizeof(num));
	for(int i=1;i<=n;i++)if(dfn[i]==0)tarjan(i);
	
    map<pair<int,int>,bool>mp; vector<int>rd(cnt+1);
	for(int i=1;i<=n;i++)for(int j:G1[i])
    {
        int x=scc[i],y=scc[j];
        if(x!=y && !mp[{x,y}])G2[x].push_back(y),rd[y]++,mp[{x,y}]=1;
    }
		
	int p=0;for(int i=1;i<=cnt;i++)if(!rd[i])p++;
	
	for(int i=1;i<=cnt;i++)if(num[i]==1 && rd[i]==0)
	{
		bool flag=0;
		for(int j:G2[i])if(rd[j]==1){flag=1;break;}
		if(!flag){p--;break;}
	}
	printf("%.6lf\n", 1.0 - 1.0*p/n );	
	return 0;
}