#include <bits/stdc++.h>
#define LLI long long int
#define FOR(v, a, b) for(LLI v = (a); v < (b); ++v)
#define FORE(v, a, b) for(LLI v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(LLI v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define fst first
#define snd second
#define popcount __builtin_popcount
#define UNIQ(v) (v).erase(unique(ALL(v)), (v).end())
#define bit(i) (1LL<<(i))

#ifdef DEBUG
#include <misc/C++/Debug.cpp>
#else
#define dump(...) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}

struct Init{
  Init(){
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
}init;

template <typename Cost = int> class Edge{
public:
  int from,to;
  Cost cost;
  Edge() {}
  Edge(int to, Cost cost): to(to), cost(cost){}
  Edge(int from, int to, Cost cost): from(from), to(to), cost(cost){}

  Edge rev() const {return Edge(to,from,cost);}
  
  friend ostream& operator<<(ostream &os, const Edge &e){
    os << "(FROM: " << e.from << "," << "TO: " << e.to << "," << "COST: " << e.cost << ")";
    return os;
  }
};

template <typename T> using Graph = vector<vector<Edge<T>>>;
template <typename T> using Tree = vector<vector<Edge<T>>>;

template <typename C, typename T> void add_edge(C &g, int from, int to, T w){
  g[from].push_back(Edge<T>(from, to, w));  
}

template <typename C, typename T> void add_undirected(C &g, int a, int b, T w){
  g[a].push_back(Edge<T>(a, b, w));
  g[b].push_back(Edge<T>(b, a, w));
}



double solve(int cur, const Graph<int> &g, vector<double> &dp, int proh){
  if(dp[cur] >= 0) return dp[cur];
  double ret = 0;

  if(cur == proh){
    int n = g[cur].size();
    n -= 1;

    if(n == 0){
      return dp[cur] = INT_MAX;
    }

    vector<double> temp;
    for(auto &e : g[cur]){
      temp.push_back(solve(e.to, g, dp, proh));
    }

    ret = accumulate(ALL(temp), 0.0) - *max_element(ALL(temp));
    
    ret /= n;
    
    ret += 1;

  }else{
    int n = g[cur].size();
  
    for(auto &e : g[cur]){
      ret += solve(e.to, g, dp, proh) / n;
    }
  
    ret += 1;
  }

  return dp[cur] = ret;
}



int main(){
  int N, M;
  while(cin >> N >> M){
    Graph<int> g(N);
    vector<pair<int,int>> edges;
    REP(i,M){
      int s,t; cin >> s >> t;
      --s, --t;
      add_edge(g, s, t, 1);
      edges.emplace_back(s,t);
    }

    dump(g);

    double ans = M;

    {
      vector<double> dp(N, -1);
      dp[N-1] = 0;
      auto res = solve(0, g, dp, -1);
      chmin(ans, res);
    }
    
    REP(i,N){
      vector<double> dp(N, -1);
      dp[N-1] = 0;
      auto res = solve(0, g, dp, i);
      chmin(ans, res);
    }


    cout << fixed << setprecision(12) << ans << endl;    
  }


  return 0;
}


Measured memory_bytes: 4848