fn main() {
    let player = read_str();
    let n = read_int()[0];
    println!("{}", n - 2);
    if player == "Alice" {
        alice(n);
    } else {
        bob(n);
    }
}

fn alice(n: usize) {
    let mut g = vec![vec![]; n + 1];
    for _ in 1..n {
        let a = read_int();
        let (a, b) = (a[0], a[1]);
        g[a].push(b);
        g[b].push(a);
    }
    let mut seq = vec![];
    for _ in 2..n {
        let x = (1..=n).find(|x| g[*x].len() == 1).unwrap();
        let y = g[x][0];
        seq.push(y);
        g[x].clear();
        g[y].retain(|p| *p != x);
    }
    use util::*;
    println!("{}", seq.iter().join(" "));
}

fn bob(n: usize) {
    let seq = read_int();
    let mut deg = vec![1; n + 1];
    for a in seq.iter() {
        deg[*a] += 1;
    }
    let mut ans = vec![];
    for s in seq.iter() {
        let x = (1..=n).find(|v| deg[*v] == 1).unwrap();
        ans.push((*s, x));
        deg[*s] -= 1;
        deg[x] -= 1;
    }
    let p = (1..=n).filter(|v| deg[*v] > 0).collect::<Vec<_>>();
    ans.push((p[0], p[1]));
    for (a, b) in ans {
        println!("{a} {b}");
    }
}

fn read_str() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    String::from(s.trim())
}

fn read_int() -> Vec<usize> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().split_whitespace().flat_map(|s| s.parse()).collect()
}
mod util {
    pub trait Join {
        fn join(self, sep: &str) -> String;
    }

    impl<T, I> Join for I
    where
        I: Iterator<Item = T>,
        T: std::fmt::Display,
    {
        fn join(self, sep: &str) -> String {
            let mut s = String::new();
            use std::fmt::*;
            for (i, v) in self.enumerate() {
                if i > 0 {
                    write!(&mut s, "{}", sep).ok();
                }
                write!(&mut s, "{}", v).ok();
            }
            s
        }
    }
}