#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <iomanip>
#include <limits>
#include <list>
#include <queue>
#include <tuple>
#include <map>
#include <stack>
#include <set>
using namespace std;
#define MOD (long long int)(1e9+7)
#define ll long long int
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define reps(i,n) for(int i=1; i<=(int)(n); i++)
#define REP(i,n) for(int i=n-1; i>=0; i--)
#define REPS(i,n) for(int i=n; i>0; i--)
#define INF (int)(1123456789)
#define LINF (long long int)(112345678901234567)
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
#define all(v) v.begin(), v.end()

const int N = (int)3e5;

ll mpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = mpow(a,b/2); return memo*memo%MOD;}
  else return mpow(a,b-1) * a % MOD;
}
ll lpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = lpow(a,b/2); return memo*memo;}
  else return lpow(a,b-1) * a;
}
ll gcd(ll a, ll b){
  if(b==0) return a;
  else return gcd(b, a%b);
}
vector<ll> kaijo_memo;
ll kaijo(ll n){
  if(kaijo_memo.size() > n) return kaijo_memo[n];
  if(kaijo_memo.size() == 0) kaijo_memo.push_back(1);
  while(kaijo_memo.size() <= n) kaijo_memo.push_back(kaijo_memo[kaijo_memo.size()-1] * kaijo_memo.size() % MOD);
  return kaijo_memo[n];
}
vector<ll> gyaku_kaijo_memo;
ll gyaku_kaijo(ll n){
  if(gyaku_kaijo_memo.size() > n) return gyaku_kaijo_memo[n];
  if(gyaku_kaijo_memo.size() == 0) gyaku_kaijo_memo.push_back(1);
  while(gyaku_kaijo_memo.size() <= n) gyaku_kaijo_memo.push_back(gyaku_kaijo_memo[gyaku_kaijo_memo.size()-1] * mpow(gyaku_kaijo_memo.size(), MOD-2) % MOD);
  return gyaku_kaijo_memo[n];
}

ll nCr(ll n, ll r){
  if(n == r) return 1;//0個の丸と-1個の棒みたいな時に時に効く？不安.
  if(n < r || r < 0) return 0;
  ll ret = 1;
  ret *= kaijo(n); ret %= MOD;
  ret *= gyaku_kaijo(r); ret %= MOD;
  ret *= gyaku_kaijo(n-r); ret %= MOD;
  return ret;
}

int n,m;
vector<int> G[1000];
double dp[1000],p[1000],dp2[1000];
void func(int now){
  if(now == n-1){
    rep(i,n){
      dp[i] = 0.0;
      p[i] = 0.0;
    }
    p[0] = 1.0;
  }

  for(auto itr = G[now].begin(); itr != G[now].end(); itr++){
    int to = *itr;
    dp[now] += (dp[to] + 1.0) / G[now].size();
  }
  if(now != 0) func(now-1);
}

void func2(int now, double dp_val, bool init){
  if(init){
    rep(i,n){
      dp2[i] = dp[i];
    }
    dp2[now] = dp_val;
    func2(now-1,0,false);
    return;
  }

  if(now == -1) return;

  dp2[now] = 0.0;
  for(auto itr = G[now].begin(); itr != G[now].end(); itr++){
    int to = *itr;
    dp2[now] += (dp2[to] + 1.0) / G[now].size();
  }
  func2(now-1,0,false);
}

int main(void){
  cin>>n>>m;
  rep(i,m){
    ll s,t;
    cin>>s>>t;s--;t--;
    G[s].push_back(t);
  }
  func(n-1);
  double ans = dp[0];
  rep(i,n){
    int best_to = -1;
    double best = -1;
    if(G[i].size() <= 1) continue;
    for(auto itr = G[i].begin(); itr != G[i].end(); itr++){
      int to = *itr;
      if(dp[to] > best){
        best_to = to;
        best = dp[to];
      }
    }

    double sum_new = 0.0;
    for(auto itr = G[i].begin(); itr != G[i].end(); itr++){
      int to = *itr;
      if(best_to == to) continue;
      sum_new += (dp[to] + 1.0) / (G[i].size() - 1.0);
    }
    func2(i,sum_new,true);

    chmin(ans,dp2[0]);
  }
  cout<<setprecision(10)<<ans<<endl;
  return 0;
}


Measured memory_bytes: 1408