#include <bits/stdc++.h>
#define whlie while
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define rep(i,N) for(int i = 0; i < (N); i++)
#define repr(i,N) for(int i = (N) - 1; i >= 0; i--)
#define rep1(i,N) for(int i = 1; i <= (N) ; i++)
#define repr1(i,N) for(int i = (N) ; i > 0 ; i--)
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
using namespace std; void solve();
using ll = long long; using vl = vector<ll>;
using vi = vector<int>; using vvi = vector< vector<int> >;
constexpr int inf = 1001001001;
constexpr ll infLL = (1LL << 61) - 1;
struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(7);} } iosetupnya;
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename T, typename U> ostream& operator <<(ostream& os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<typename T, typename U> istream& operator >>(istream& is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator <<(ostream& os, const vector<T> &v) { int s = (int)v.size(); rep(i,s) os << (i ? " " : "") << v[i]; return os; }
template<typename T> istream& operator >>(istream& is, vector<T> &v) { for(auto &x : v) is >> x; return is; }
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << "\n";} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#ifdef NyaanDebug
  #include "NyaanDebug.h"
  #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0)
  #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);cout << endl;} while(0)
#else
  #define trc(...)
  #define trca(...)
  int main(){solve();}
#endif
using P = pair<ll,ll>; using vp = vector<P>;
constexpr int MOD = /**/ 1000000007; //*/ 998244353;
/////////

void solve(){

  ini(N , M);
  // g 普通のグラフ h 逆辺グラフ
  vvi g(N) , h(N);
  rep(i , M){
    ini(s , t); s--; t--;
    g[s].pb(t); h[t].pb(s);
  }
  
  vector<double> arrive(N, 0.0) , prob(N , 0.0) , inv(N , 0.0);

  // 到着確率
  arrive[0] = 1.0;
  rep(i , N){
    each(x , g[i]){
      arrive[x] += arrive[i] / (g[i].size());
    }
  }

  /*
  // 到着回数の期待値
  rep(i , N){
    each(x , g[i]){
      prob[x] += (prob[i] + 1) * (arrive[i] / g[i].size() ) / arrive[x];
    }
  }
  */

  // 逆辺
  repr(i , N){
    each(x , h[i]){
      inv[x] += (inv[i] + 1) / g[x].size();
    }
  }

  rep(i , N) trc(g[i]);

  trc(arrive);
  trc(inv);
  
  double ans = inv[0];
  // ふさぐ辺の始点  
  rep(i , N){
    // 1本しか路が出ていないときは塞げない
    if(g[i].size() == 1) continue;
  
    each(x , g[i]){
      // 今の期待値はinv[i]
      double nxt_inv = ( inv[i] * sz(g[i]) - (1 + inv[x]) ) / (sz(g[i]) - 1);
      double cur = inv[0] - (inv[i] - nxt_inv) * arrive[i];
      amin(ans , cur);
    }
  }
  out(ans);
  
}

Measured memory_bytes: 2560