#include <bits/stdc++.h>
using namespace std;
#define INF 1<<30
#define endl '\n'
#define maxn 100005
#define tc printf("Case %d: ", cs)
#define tcn printf("Case %d:\n", cs);
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);

#define dbg1(x) cerr << #x << " = " << x << endl;
#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
#define dbg3(x, y, z) cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
#define dbg4(w,x, y, z) cerr << #w << " = " << w << ", " <<#x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;

template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
	return os << "(" << p.first << ", " << p.second << ")";
}

template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
	os << "{";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin() ) os << ", ";
		os << *it;
	}
	return os << "}";
}

template < typename T >
ostream &operator << ( ostream & os, const set< T > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin()) os << ", ";
		os << *it;
	}
	return os << "]";
}

template < typename F, typename S >
ostream &operator << ( ostream & os, const map< F, S > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin() ) os << ", ";
		os << it -> first << " = " << it -> second ;
	}
	return os << "]";
}

#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)

clock_t tStart = clock();
#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)

void faltu () { cerr << endl; }

template <typename T>
void faltu( T a[], int n ) {
	for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
	cerr << endl;
}

template <typename T, typename ... hello>
void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less 
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

/**___________________________________________________**/



int main()
{
	FASTIO
	/*
#ifndef ONLINE_JUDGE
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
	freopen("error.txt", "w", stderr);
#endif
//*/
	int n, m;
	cin >> n >> m;
	bool graph[n][n];
	for (int i = 0; i  < n; i++)
		for (int j = 0; j < n; j++) graph[i][j] = false;

	for (int i = 0; i < m; i++) {
		int u, v;
		cin >> u >> v;
		--u;
		--v;
		graph[u][v] = true;
	}

	long double E[n], p[n];
	for (int i = 0; i < n; i++) {
		E[i] = p[i] = 0;
	}
	p[0] = 1;
	int deg[n];
	for (int i = 0; i < n; i++) {
		deg[i] = 0;
		for (int j = 0; j < n; j++) {
			if (graph[i][j]) deg[i]++;
		}
	}

	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			if (!graph[i][j]) continue;
			p[j] += p[i] / deg[i];
		}
	}
	for (int i = n - 1; i >= 0; i--) {
		for (int j = 0; j < i; j++) {
			if (!graph[j][i]) continue;
			E[j] += (E[i] + 1) / deg[j];
		}
	}

	long double ans = E[0];
	for (int i = 0; i < n; i++) {
		if (deg[i] == 1)continue;
		for (int j = i + 1; j < n; j++) {
			if (!graph[i][j]) continue;
			long double val = E[0];
			val -= E[i] * p[i];
			long double curE = E[i];
			curE -= 1;
			curE -= E[j] / deg[i];
			curE *= deg[i];
			curE /= (deg[i] - 1);
			curE += 1;
			val += curE * p[i];
			ans = min(ans, val);
		}
	}
	cout << setprecision(20) << ans << endl;
}

Measured memory_bytes: 640