// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define bit(n) (1LL<<(n))
// functions
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;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(20);}
} fast_io_;

struct Graph{
  int n = 0;
  vector<vector<int> > edge;
  vector<int> in_deg;
  explicit Graph(int n): n(n){
    edge.resize(n);
    in_deg.resize(n, 0);
  }
  void adde(int at, int to){
    edge[at].push_back(to);
    in_deg[to]++;
  }
  vector<int> topological_sort(){
    stack<int> st;
    for(int i = 0; i < n; i++){
      if(in_deg[i] == 0)st.push(i);
    }
    vector<int> res;
    while(st.size()){
      int at = st.top(); st.pop();
      res.push_back(at);
      for(int j: edge[at]){
        in_deg[j]--;
        if(in_deg[j] == 0)st.push(j);
      }
    }

    return res;
  }
};


vector<int> v[610], u[610];
double dp[610], dp2[610];

int main(int argc, char const* argv[])
{
  int n, m; cin >> n >> m;
  rep(i, m){
    int s, t; cin >> s >> t;
    s--; t--;
    v[s].pb(t);
    u[t].pb(s);
  }
  dp[n-1] = 0.;
  for(int i = n - 2; i >= 0; i--){
    dp[i] = 1.;
    for(auto e: v[i]){
      dp[i] += dp[e] / sz(v[i]);
    }
  }
  double res = dp[0];
  rep(i, n - 1){
    if(sz(v[i]) == 1)continue;
    double maxi = -1.;
    int idx = -1;
    for(auto e: v[i]){
      if(maxi < dp[e]){
        maxi = dp[e];
        idx = e;
      }
    }
    dp2[n-1] = 0.;
    for(int k = n - 2; k >= 0; k--){
      int d = (k == i) ? 1: 0;
      dp2[k] = 1.;
      for(auto e: v[k]){
        if(i == k && e == idx)continue;
        dp2[k] += dp2[e] / (sz(v[k]) - d);
      }
    }
    res = min(res, dp2[0]);
  }
  cout << res << endl;
  return 0;
}


Measured memory_bytes: 2560