#[macro_use]
pub mod basic_stdin {
use std::str::FromStr;

pub fn read<T: FromStr>() -> T {
    use std::io::stdin;
    use std::io::Read;

    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed reading char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed parsing")
}

}

#[macro_export]
macro_rules! test_function {
    (func = $func:expr, $($input:expr => $output:expr),* $(,)*) => {
        $(
            assert_eq!($func(std::io::Cursor::new($input)) , $output);
        )*
    };
}

#[macro_export]
macro_rules! input_macro {
    (string = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    (reader = $s:expr, $($r:tt)*) => {
        let reader = std::io::BufReader::new($s);
        let mut bytes = std::io::Read::bytes(reader);
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

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

#[macro_export]
macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

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

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

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

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

type Graph = Vec<Vec<usize>>;

fn main() {
    let stdin = std::io::stdin();
    let ret = solve(stdin.lock());

    println!("{}", ret);
}

fn dfs(graph: &Graph, visit: &mut Vec<bool>, start: usize, c: usize) -> usize {
    let mut count = c;
    if visit[start] {
        return count;
    }

    visit[start] = true;

    if visit.iter().all(|&x| x) {
        count += 1;
    }

    for new_start in &graph[start] {
        count = dfs(graph, visit, *new_start, count);
    }

    visit[start] = false;

    return count;
}

fn solve<T: std::io::Read>(reader: T) -> usize {
    input_macro! {
        reader = reader,
        n: usize,
        m: usize,
        edges: [(usize1, usize1); m],
    }

    let mut graph = Graph::with_capacity(n);
    for _ in 0..n {
        graph.push(Vec::new());
    }
    for e in edges {
        graph[e.0].push(e.1);
        graph[e.1].push(e.0);
    }

    let mut visit: Vec<bool> = Vec::with_capacity(n);
    visit.resize(n, false);

    let ans = dfs(&graph, &mut visit, 0, 0);
    ans
}

#[cfg(test)]
mod tests {

    #[test]
    fn test_solve_function() {
        atcorder::test_function! {
            func = super::solve,
            "3 3 1 2 1 3 2 3" => 2,
            "7 7 1 3 2 7 3 4 4 5 4 6 5 6 6 7" => 1,
        }
    }
}


Measured memory_bytes: 4352