#include <stdio.h>
#include <iostream>
#include <cstdio>
#include <algorithm> 
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <list>
#include <utility>
#include <set>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <bitset>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <random>

using namespace std;

static const double EPS = 1e-9;
template<class T> bool INRANGE(T x, T a, T b) { return a <= x && x <= b; }
template<class T> void amin(T &a, T v) { if (a > v) a = v; }
template<class T> void amax(T &a, T v) { if (a < v) a = v; }
int ROUND(double x) { return (int)(x + 0.5); }
bool ISINT(double x) { return fabs(ROUND(x) - x) <= EPS; }
bool ISEQUAL(double x, double y) { return fabs(x - y) <= EPS * max(1.0, max(fabs(x), fabs(y))); }
double SQSUM(double x, double y) { return x * x + y * y; }
#define PI  (acos(-1))
#define ARRAY_NUM(a) (sizeof(a)/sizeof(a[0])) 
#define NG (-1)
#define BIG ((int)1e9+10)
#define BIGLL ((ll)4e18)
#define SZ(a) ((int)(a).size())
#define SQ(a) ((a)*(a))
typedef unsigned long long ull;
typedef long long ll;

using namespace std;
typedef long long ll;

// modint: mod 計算を int を扱うように扱える構造体
template<int MOD>
struct ModInt {
	long long val;
	constexpr ModInt(long long v = 0) noexcept : val(v % MOD) {
		if (val < 0) v += MOD;
	}
	constexpr int getmod() { return MOD; }
	constexpr ModInt operator - () const noexcept {
		return val ? MOD - val : 0;
	}
	constexpr ModInt operator + (const ModInt& r) const noexcept { return ModInt(*this) += r; }
	constexpr ModInt operator - (const ModInt& r) const noexcept { return ModInt(*this) -= r; }
	constexpr ModInt operator * (const ModInt& r) const noexcept { return ModInt(*this) *= r; }
	constexpr ModInt operator / (const ModInt& r) const noexcept { return ModInt(*this) /= r; }
	constexpr ModInt& operator += (const ModInt& r) noexcept {
		val += r.val;
		if (val >= MOD) val -= MOD;
		return *this;
	}
	constexpr ModInt& operator -= (const ModInt& r) noexcept {
		val -= r.val;
		if (val < 0) val += MOD;
		return *this;
	}
	constexpr ModInt& operator *= (const ModInt& r) noexcept {
		val = val * r.val % MOD;
		return *this;
	}
	constexpr ModInt& operator /= (const ModInt& r) noexcept {
		long long a = r.val, b = MOD, u = 1, v = 0;
		while (b) {
			long long t = a / b;
			a -= t * b; swap(a, b);
			u -= t * v; swap(u, v);
		}
		val = val * u % MOD;
		if (val < 0) val += MOD;
		return *this;
	}
	constexpr bool operator == (const ModInt& r) const noexcept {
		return this->val == r.val;
	}
	constexpr bool operator != (const ModInt& r) const noexcept {
		return this->val != r.val;
	}

	friend ostream& operator << (ostream &os, const ModInt<MOD>& x) noexcept {
		return os << x.val;
	}
	friend istream& operator >> (istream &is, ModInt<MOD>& x) noexcept {
		return is >> x.val;
	}
	static constexpr ModInt<MOD> modpow(const ModInt<MOD> &a, long long n) noexcept {
		if (n == 0) return 1;
		auto t = modpow(a, n / 2);
		t = t * t;
		if (n & 1) t = t * a;
		return t;
	}
};

template<class T>
vector<T> make_vector(int n, T t) {
	return vector<T>(n, t);
}

template<class ...Ts>
auto make_vector(int n, Ts ... ts) {
	return vector<decltype(make_vector(ts...))>(n, make_vector(ts...));
}

int main()
{
	int N, M;
	cin >> N >> M;

	vector < vector <int> > adj(N);

	for (int i = 0; i < M; ++i)
	{
		int s, t;
		cin >> s >> t;
		s--;
		t--;

		adj[s].push_back(t);
	}

	vector <double> e(N), p(N);

	// 始点からの到達確率pを求める
	p[0] = 1.0;
	for (int i = 0; i < N; ++i)
	{
		const int d = SZ(adj[i]);
		for (int next : adj[i])
		{
			p[next] += p[i] / d;
		}
	}

	// 何もしないときの歩数の期待値eを求める
	double shortcut = 0.0;
	for (int i = N - 1; i >= 0; --i)
	{
		const int d = SZ(adj[i]);
		if (d > 0)
		{
			double sum = 0.0;
			double hi = 0.0;	// 最も次へいくのを防ぎたい場所の歩数期待値
			for (int next : adj[i])
			{
				sum += e[next];
				amax(hi, e[next]);
			}

			e[i] = 1 + sum / d;
			if (d > 1)
			{
				double blocked = 1 + (sum - hi) / (d - 1.0);
				amax(shortcut, p[i]*(e[i]- blocked));
			}
		}
	}





	printf("%.16f\n", e[0]-shortcut);
	
	return 0;
}


Measured memory_bytes: 1408