#include<algorithm>
#include<bitset>
#include<cassert>
#include<cfloat>
#include<climits>
#include<cmath>
#include<deque>
#include<functional>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<string>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>

using namespace std;

using lint = long long;
using P = pair<int, int>;
using LLP = pair<long long, long long>;

#define REP(i, x, n) for(int i = (x), i##_len = (int)(n) ; i < i##_len ; ++i)
#define rep(i, n) for(int i = 0, i##_len = (int)(n) ; i < i##_len ; ++i)
#define reps(i, n) for(int i = 1, i##_len = (int)(n) ; i <= i##_len ; ++i)
#define rrep(i, n) for(int i = (int)(n) - 1 ; i >= 0 ; --i)
#define rreps(i, n) for(int i = (int)(n) ; i > 0 ; --i)
#define SORT(x) sort((x).begin(), (x).end())
#define SORT_INV(x) sort((x).rbegin(), (x).rend())
#define REVERSE(x) reverse((x).begin(), (x).end())
#define TWINS(x) cout << ((x) ? "Yay!" : ":(") << '\n'
#define endl '\n'

constexpr int IINF = (1 << 30) - 1;
constexpr long long LLINF = 1LL << 61;
constexpr double EPS = 1e-10;

constexpr int dx4[] = {1, 0, -1, 0}, dy4[] = {0, 1, 0, -1};
constexpr int dx8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dy8[] = {0, -1, -1, -1, 0, 1, 1, 1};

template<typename T>
bool chmax(T& a, T b){
    if(a < b){
        a = b;
        return true;
    }
    return false;
}

template<typename T>
bool chmin(T& a, T b){
    if(b < a){
        a = b;
        return true;
    }
    return false;
}

typedef vector<double> vec;
typedef vector< vec > mat;

vec gauss_jordan(const mat& A, const vec& b){
    int n = A.size();
    mat B(n, vec(n + 1));
    for(int i = 0 ; i < n ; ++i)
    for(int j = 0 ; j < n ; ++j) B[i][j] = A[i][j];
    for(int i = 0 ; i < n ; ++i) B[i][n] = b[i];
    for(int i = 0 ; i < n ; ++i){
        int pivot = i;
        for(int j = i ; j < n ; ++j){
            if(abs(B[j][i]) > abs(B[pivot][i])) pivot = j;
        }
        swap(B[i], B[pivot]);
        if(abs(B[i][i]) < EPS) return vec();
        for(int j = i + 1 ; j <= n ; ++j) B[i][j] /= B[i][i];
        for(int j = 0 ; j < n ; ++j){
            if(i != j){
                for(int k = i + 1 ; k <= n ; ++k) B[j][k] -= B[j][i] * B[i][k];
            }
        }
    }
    vec x(n);
    for(int i = 0 ; i < n ; ++i) x[i] = B[i][n];
    return x;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    int n, m;
    cin >> n >> m;

    vector< vector<int> > g(n);
    rep(i, m){
        int s, t;
        cin >> s >> t;
        g[--s].emplace_back(--t);
    }

    mat A(n, vec(n, 0.0));
    vec b(n);
    rep(i, n - 1){
        double T = g[i].size();
        A[i][i] = T;
        for(auto to : g[i]){
            A[i][to] -= 1.0;
        }
        b[i] = T;
    }
    A[n - 1][n - 1] = 1.0;
    b[n - 1] = 0.0;

    vec e = gauss_jordan(A, b);

    assert(!e.empty());

    vec p(n);
    p[0] = 1.0;
    rep(i, n){
        double T = g[i].size();
        for(auto to : g[i]){
            p[to] += p[i] / T;
        }
    }

    double ans = e[0];

    double D = 1e10;

    rep(i, n){
        if((int)g[i].size() <= 1){
            continue;
        }
        sort(g[i].begin(), g[i].end(), [&](int i, int j){ return e[i] > e[j]; });
        double T = g[i].size();
        double d = e[g[i][0]] / T;
        d = -d;
        REP(j, 1, g[i].size()){
            d += e[g[i][j]] / (T - 1.0) - e[g[i][j]] / T;
        }
        chmin(D, d * p[i]);
    }

    chmin(ans, ans + D);

    cout << ans << endl;

    cout << flush;

    return 0;
}

Measured memory_bytes: 7168