use std::cmp::min;
use std::collections::HashSet;

fn main() {
    let mut nk = String::new();
    std::io::stdin().read_line(&mut nk).ok();
    let nk: Vec<usize> = nk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nk[0];
    let k = nk[1];
    let mut ab: Vec<Vec<usize>> = vec![vec![]; n];
    for _ in 0..n-1 {
        let mut aab = String::new();
        std::io::stdin().read_line(&mut aab).ok();
        let aab: Vec<usize> = aab.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
        ab[aab[0] - 1].push(aab[1] - 1);
        ab[aab[1] - 1].push(aab[0] - 1);
    }
    
    if n < k {
        println!("{}", -1);
        return;
    }

    let mut dists: Vec<usize> = vec![1000000; n];
    dists[0] = 0;
    let mut checked: HashSet<usize> = HashSet::new();
    checked.insert(0);
    let mut vertices: Vec<usize> = vec![];
    vertices.push(0);
    let mut dist: usize = 1;
    while vertices.len() > 0 {
        let mut nexts: Vec<usize> = vec![];
        vertices.iter().for_each(|v| {
            ab[*v].iter().for_each(|i| {
                if checked.contains(i) { return; }
                nexts.push(*i);
                checked.insert(*i);
                dists[*i] = min(dists[*i], dist);
            });
        });
        vertices = nexts;
        dist += 1;
    }
    dists.sort();
    let max_move: usize = *dists.iter().take(k).max().unwrap();
    println!("{}", dists.iter().take(k).filter(|i| **i == max_move).count() * max_move);
}