// https://atcoder.jp/contests/abc144/tasks/abc144_f
//
#![allow(unused_imports)]
use std::io::*;
use std::fmt::*;
use std::str::*;
use std::cmp::*;
use std::collections::*;

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };

    ($iter:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, [ next / $t:tt ]) => {
        {
            let len = read_value!($iter, usize);
            (0..len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
        }
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

#[allow(unused_macros)]
macro_rules! dvec {
    ($t:expr ; $len:expr) => {
        vec![$t; $len]
    };

    ($t:expr ; $len:expr, $($rest:expr),*) => {
        vec![dvec!($t; $($rest),*); $len]
    };
}

#[allow(unused_macros)]
macro_rules! ifv {
    ($t:expr, $a:expr, $b: expr) => {
        if $t { $a } else { $b }
    }
}

#[allow(unused_macros)]
macro_rules! fill {
    ($t:expr, $v:expr) => {
        for i in 0..$t.len() {
            $t[i] = $v;
        }
    };
}

#[allow(unused_macros)]
macro_rules! join {
    ($t:expr, $glue:expr) => {
        $t.into_iter().map(|w| w.to_string()).collect::<Vec<_>>().join($glue)
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}

const INF: f64 = 1e12;

#[derive(PartialEq,PartialOrd)]
struct Of64(f64);

impl Eq for Of64 {}

impl Ord for Of64 {
    fn cmp(&self, other: &Of64) -> Ordering {
        self.partial_cmp(other).unwrap()
    }
}

fn minf(a: f64, b: f64) -> f64 {
    if a <= b {
        a
    } else {
        b
    }
}

fn solve(f: usize, graph: &Vec<Vec<usize>>) -> f64 {
    let n = graph.len();
    let mut dp = vec![0.0f64; n];
    for i in (0..n-1).rev() {
        let mut total = 0.0;
        let mut wmax = 0.0;
        for &to in &graph[i] {
            total += dp[to];
            wmax = f64::max(wmax, dp[to]);
        }
        let cn = graph[i].len();
        let cnf = cn as f64;
        if f == i && cnf >= 2.0 {
            dp[i] = (total - wmax) / (cnf - 1.0);
        } else {
            dp[i] = total / cnf;
        }
        dp[i] += 1.0;
    }
    dp[0]
}

fn main() {
    input! {
        n: usize, m: usize,
        edges: [(usize1, usize1); m]
    };

    let mut graph = vec![vec![]; n];
    for (u, v) in edges {
        graph[u].push(v);
    }
    let mut best = INF;
    for i in 0..n-1 {
        best = f64::min(best, solve(i, &graph));
    }
    println!("{:.9}", best);
}


Measured memory_bytes: 12540