#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<set>
#include<queue>
#include<stack>
#include<bitset>
#include<functional>
#include<map>
#include<iomanip>
#include<limits>
#include<unordered_set> 
#include<cmath>
#include <numeric>
#include <array>
using namespace std;
//long long p = 998244353;
long long p = 1000000007;
#define int long long
#define vel vector<long long>
#define vvel vector<vel>
#define rep(i,n) for(int i=0;i<n;i++)
#define sor(v) sort(v.begin(),v.end())
#define mmax(a,b) a=max(a,b)
#define mmin(a,b) a=min(a,b)
#define mkp make_pair
#define pin pair<int,int>
#define qin pair<pin,int>
#define V vector
#define Endl endl
#define veb vector<bool>
#define fcout cout << fixed << setprecision(15)
#define rev(s) reverse(s.begin(),s.end())
#define lower(h,val) lower_bound(h.begin(),h.end(),val)-h.begin()
#define upper(h,val) upper_bound(h.begin(),h.end(),val)-h.begin()
int max_kai = 150000;
vel kai(max_kai, 1);
vel inv_kai;
int rui(int a, int n, int mod) {
    if (n == 0) { return 1 % mod; }
    int x = rui(a, n / 2, mod);
    x *= x; x %= mod;
    if (n % 2 == 1) { x *= a; x %= mod; }
    return x;
}
vel pa;
int root(int x) {
    if (pa[x] == -1) { return x; }
    int ans = root(pa[x]); pa[x] = ans;
    return ans;
}
void marge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) { pa[x] = y; }
}
int gcd(int x, int y) {
    if (x < y) { return gcd(y, x); }
    if (y == 0) { return x; }
    return gcd(y, x % y);
}
long long modinv(long long a, long long m) {
    long long b = m, u = 1, v = 0;
    while (b) {
        long long t = a / b;
        a -= t * b; swap(a, b);
        u -= t * v; swap(u, v);
    }
    u %= m;
    if (u < 0) u += m;
    return u;
}
vel uni(vel x) {
    if (x.size() == 0) { return x; }
    sor(x);
    int n = x.size();
    vel ans(1, x[0]);
    for (int j = 1; j < n; j++) {
        if (x[j - 1] != x[j]) { ans.push_back(x[j]); }
    }
    x = ans;
    return x;
}
void pr(vel& v) {
    int n = v.size();
    if (n != 0) {
        cout << v[0];
        rep(i, n - 1) {
            cout << " " << v[i + 1];
        }
        cout << endl;
    }
}
int sol(int x, int k) {
    if (x == 0 || k == 0) { return 0; }
    return x + sol(x / 2, k - 1);
}
vel pri(int n) {
    veb ans(n, true);
    vel prime;
    for (int j = 2; j < n; j++) {
        if (ans[j]) {
            prime.push_back(j);
            for (int k = 2; j * k < n; k++) {
                ans[j * k] = false;
            }
        }
    }
    return prime;
}
V<double> solve2(vel a, vel b, int n) {
    vvel way(n);
    int m = a.size();
    rep(i, m) { way[a[i]].push_back(b[i]);}
    V<double> dp(n, 0);
    for (int i = n - 2; i >= 0; i--) {
        for (auto x : way[i]) {
            dp[i] += dp[x] / way[i].size();
        }
        dp[i]++;
    }
    return dp;
}

V<double> solve(vel a, vel b, int n) {
    vvel way(n);
    int m = a.size();
    vel count(n, 0);
    rep(i, m) { way[a[i]].push_back(b[i]); count[b[i]]++; }
    V<double> dp(n, 0); dp[0] = 1;
    rep(i, n - 1) {
        for (auto x : way[i]) {
            dp[x] += dp[i] / way[i].size();
        }
    }
    return dp;
}
signed main() {
    int n, m; cin >> n >> m;
    vel a(m); vel b(m);
    vvel way(n);
    rep(i, m) { cin >> a[i] >> b[i]; a[i]--; b[i]--; way[a[i]].push_back(b[i]); }
    V<double> E = solve(a, b, n);
    V<double> F = solve2(a, b, n);
    double ans = F[0];
    rep(i, n) {
        V<double> next_score;
        if (way[i].size() > 1) {
            for (auto x : way[i]) {
                next_score.push_back(F[x]);
            }
            sor(next_score);
            double sum0 = 0;
            double sum1 = 0;
            int sz = next_score.size();
            rep(i, sz) {
                sum0 += next_score[i];
                if (i != sz-1){ sum1 += next_score[i]; }
            }
            sum0 *= E[i];
            sum1 *= E[i];
            double qans = F[0] - (sum0 / sz) + (sum1 / (sz - 1));
            mmin(ans, qans);
        }
    }
    fcout << ans << endl;
    return 0;
}


Measured memory_bytes: 11540