#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, a, b) for(int i = a; i < b; i++)
#define rrep(i, a, b) for(int i = b - 1; i >= a; i--)
#define ALL(a) a.begin(), a.end()
#define pii pair<int,int>
#pragma GCC optimize("Ofast")
#define pcnt __builtin_popcount
#define buli(x) __builtin_popcountll(x)
#define pb push_back
#define mp make_pair
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
template<class T>bool chmax(T &a, const T &b) {if(a<b){a = b; return 1;} return 0; };
template<class T>bool chmin(T &a, const T &b) {if(a>b){a = b; return 1;} return 0; };
inline void IN(void){return;}
template <typename First, typename... Rest> void IN(First& first, Rest&... rest){cin >> first;IN(rest...);return;}
inline void OUT(void){cout << "\n";return;}
template <typename First, typename... Rest> void OUT(First first, Rest... rest){cout << first << " ";OUT(rest...);return;}
const double EPS = 1e-9;
const int mod = 1e9 + 7;
const int INF = 1e9;
const long long LLINF = 1e18;
long long lcm(ll a, ll b){return a * b / __gcd(a,b);}
struct IoSetup { IoSetup() {
    cin.tie(nullptr);ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
} } iosetup;
template< int mod > struct ModInt {
    int x; ModInt() : x(0) {}
    ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}
    ModInt &operator+=(const ModInt &p) {if((x += p.x) >= mod) x -= mod;return *this;}
    ModInt &operator-=(const ModInt &p) {if((x += mod - p.x) >= mod) x -= mod;return *this;}
    ModInt &operator*=(const ModInt &p) {x = (int) (1LL * x * p.x % mod);return *this;}
    ModInt &operator/=(const ModInt &p) {*this *= p.inverse();return *this;}
    ModInt operator-() const { return ModInt(-x); }
    ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }
    ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }
    ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }
    ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }
    bool operator==(const ModInt &p) const { return x == p.x; }
    bool operator!=(const ModInt &p) const { return x != p.x; }
    ModInt inverse() const {int a = x, b = mod, u = 1, v = 0, t;
    while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); }return ModInt(u);}
    ModInt pow(int64_t n) const {ModInt ret(1), mul(x); while(n > 0) {if(n & 1) ret *= mul;mul *= mul;n >>= 1;}return ret;}
    friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x;}
    friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); }
    static int get_mod() { return mod; }
}; using modint = ModInt< mod >;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

template< typename T > struct edge {
   int src, to; T cost;
   edge(int to, T cost) : src(-1), to(to), cost(cost) {}
   edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}
   edge &operator=(const int &x) { to = x; return *this;}
   operator int() const { return to; }
};
template< typename T > using Edges = vector< edge< T > >;
template< typename T > using WeightedGraph = vector< Edges< T > >;
using UnWeightedGraph = vector< vector< int > >;
template< typename T > using Matrix = vector< vector< T > >;

int main(){
    iosetup;
    int N, M; cin >> N >> M;
    UnWeightedGraph g(N);
    rep(i, 0, M){
        int s, t; cin >> s >> t; s--, t--;
        g[s].push_back(t);
    }
    // rep(i, 0, N) sort(ALL(g[i]));
    vector<double> dp(N, 0);
    map<int,int> f;
    rrep(j, 0, N-1){
        int S = g[j].size();
        for(auto nv: g[j]) dp[j] += (1.0 + dp[nv]) / (double)S;
    }
    double ans = dp[0];
    rep(i, 0, N - 1){
        double M = 0;
        int idx = -1;
        if(g[i].size() == 1){
            f[i] = idx;
            continue;
        };
        for(auto e: g[i]){
            if(dp[e] > M){
                M = dp[e];
                idx = e;
            }
        }
        f[i] = idx;
    }
    rep(i, 0, N - 1){
        vector<double> tdp(N, 0);
        tdp[N-1] = 0;
        bool F = false;
        rrep(j, 0, N-1){
            int S = g[j].size();
            bool flag = 0;
            if(i == j) flag = true;
            if(flag && S == 1) {
                F = true;
                break;
            }
            if(flag) S--;
            for(auto nv: g[j]){
                if(flag && f[j] == nv) continue;
                tdp[j] += (1 + tdp[nv]) / S;
            }
        }
        if(F) continue;
        //rep(j, 0, N) cerr << j << " " << tdp[j] << endl;
        chmin(ans, tdp[0]);
    }
    cout << ans << endl;
    return 0;
}


Measured memory_bytes: 1408