#![allow(unused_imports, unused_macros)]

use kyoproio::*;
use std::{
    collections::*,
    io::{self, prelude::*},
    iter, mem,
};

fn run<I: Input, O: Write>(mut kin: I, mut out: O) {
    let (n, k): (usize, usize) = kin.input();
    let mut g = AdjListBuilder::new(n + 1);
    g.extend_bi_edges(kin.iter::<(usize, usize)>().take(n - 1));
    if k > n {
        outln!(out, "-1");
        return;
    }
    let g = g.build();
    eout!("{:?}", g);
    let mut que = VecDeque::new();
    que.push_back(1);
    let mut dist = vec![!0; n + 1];
    dist[1] = 0;
    let mut ans = 0i64;
    let mut cnt = 0;
    while let Some(u) = que.pop_front() {
        ans += dist[u];
        cnt += 1;
        if cnt >= k {
            break;
        }
        for &v in &g[u] {
            if dist[v] == !0 {
                dist[v] = dist[u] + 1;
                que.push_back(v);
            }
        }
    }
    outln!(out, "{}", ans);
}

use std::{
    // iter,
    ops::{Index, IndexMut},
};
pub struct AdjList(JaggedArray<usize>);
impl AdjList {
    pub fn len(&self) -> usize {
        self.0.len()
    }
    pub fn iter(&self) -> AdjListIter {
        AdjListIter(self.0.iter())
    }
}
impl Index<usize> for AdjList {
    type Output = [usize];
    fn index(&self, i: usize) -> &[usize] {
        &self.0[i]
    }
}
impl std::fmt::Debug for AdjList {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_map().entries(self.iter().enumerate()).finish()
    }
}
pub struct AdjListIter<'a>(Iter<'a, usize>);
impl<'a> Iterator for AdjListIter<'a> {
    type Item = &'a [usize];
    fn next(&mut self) -> Option<Self::Item> {
        self.0.next()
    }
}
pub struct AdjListBuilder(Builder<usize>);
impl AdjListBuilder {
    pub fn new(n: usize) -> Self {
        Self(Builder::new(n))
    }
    pub fn with_capacity(n: usize, cap: usize) -> Self {
        Self(Builder::with_capacity(n, cap))
    }
    pub fn edge(&mut self, u: usize, v: usize) {
        self.0.push(u, v);
    }
    pub fn bi_edge(&mut self, u: usize, v: usize) {
        self.edge(u, v);
        self.edge(v, u);
    }
    pub fn extend_bi_edges<I: IntoIterator<Item = (usize, usize)>>(&mut self, it: I) {
        self.0.extend(
            it.into_iter()
                .flat_map(|(u, v)| iter::once((u, v)).chain(iter::once((v, u)))),
        );
    }
    pub fn build(self) -> AdjList {
        AdjList(self.0.build())
    }
}
impl Extend<(usize, usize)> for AdjListBuilder {
    fn extend<T: IntoIterator<Item = (usize, usize)>>(&mut self, iter: T) {
        self.0.extend(iter)
    }
}

pub struct JaggedArray<T> {
    heads: Box<[usize]>,
    buf: Box<[T]>,
}
impl<T> JaggedArray<T> {
    pub fn len(&self) -> usize {
        self.heads.len() - 1
    }
    pub fn is_empty(&self) -> bool {
        self.heads.is_empty()
    }
    pub fn iter<'a>(&'a self) -> Iter<'a, T> {
        Iter { a: self, i: 0 }
    }
}
impl<T> Index<usize> for JaggedArray<T> {
    type Output = [T];
    fn index(&self, i: usize) -> &[T] {
        if let Some([l, r, ..]) = self.heads.get(i..) {
            unsafe { self.buf.get_unchecked(*l..*r) }
        } else {
            &[]
        }
    }
}
impl<T> IndexMut<usize> for JaggedArray<T> {
    fn index_mut(&mut self, i: usize) -> &mut [T] {
        if let Some([l, r, ..]) = self.heads.get(i..) {
            unsafe { self.buf.get_unchecked_mut(*l..*r) }
        } else {
            &mut []
        }
    }
}
impl<'a, T> IntoIterator for &'a JaggedArray<T> {
    type Item = &'a [T];
    type IntoIter = Iter<'a, T>;
    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}
pub struct Iter<'a, T> {
    a: &'a JaggedArray<T>,
    i: usize,
}
impl<'a, T> Iterator for Iter<'a, T> {
    type Item = &'a [T];
    fn next(&mut self) -> Option<Self::Item> {
        if self.i < self.a.len() {
            let res = &self.a[self.i];
            self.i += 1;
            Some(res)
        } else {
            None
        }
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        let rest = self.a.len() - self.i;
        (rest, Some(rest))
    }
}
pub struct Builder<T> {
    heads: Vec<usize>,
    nodes: Vec<(T, usize)>,
}
impl<T> Builder<T> {
    pub fn new(n: usize) -> Self {
        Self::with_capacity(n, 0)
    }
    pub fn with_capacity(n: usize, cap: usize) -> Self {
        Self {
            heads: vec![!0; n + 1],
            nodes: Vec::with_capacity(cap),
        }
    }
    pub fn push(&mut self, i: usize, x: T) {
        self.nodes.push((x, self.heads[i]));
        self.heads[i] = self.nodes.len() - 1;
    }
    pub fn build(mut self) -> JaggedArray<T> {
        let mut buf_i = self.nodes.len();
        let mut buf = Vec::<T>::with_capacity(buf_i);
        let buf_p = buf.as_mut_ptr();
        *self.heads.last_mut().unwrap() = buf_i;
        unsafe {
            for h in self.heads.iter_mut().rev().skip(1) {
                let mut nodes_i = *h;
                while let Some((x, next)) = self.nodes.get(nodes_i) {
                    buf_i -= 1;
                    buf_p.add(buf_i).copy_from_nonoverlapping(x, 1);
                    nodes_i = *next;
                }
                *h = buf_i;
            }
            self.nodes.set_len(0);
            buf.set_len(buf.capacity());
        }
        JaggedArray {
            heads: self.heads.into(),
            buf: buf.into(),
        }
    }
}
impl<T> Extend<(usize, T)> for Builder<T> {
    fn extend<I: IntoIterator<Item = (usize, T)>>(&mut self, iter: I) {
        for (i, x) in iter {
            self.push(i, x);
        }
    }
}


// -----------------------------------------------------------------------------
fn main() -> io::Result<()> {
    std::thread::Builder::new()
        .stack_size(1 << 26)
        .spawn(|| {
            run(
                KInput::new(io::stdin().lock()),
                io::BufWriter::new(io::stdout().lock()),
            )
        })?
        .join()
        .unwrap();
    Ok(())
}

#[macro_export]
macro_rules! out {
    ($($arg:tt)*) => { write!($($arg)*).unwrap(); }
}
#[macro_export]
macro_rules! outln {
    ($dst:expr $(, $($arg:tt)*)?) => {{
        writeln!($dst $(, $($arg)*)?).unwrap();
        if cfg!(debug_assertions) { $dst.flush().unwrap(); }
    }}
}
#[macro_export]
macro_rules! eout {
    ($($arg:tt)*) => { if cfg!(debug_assertions) { eprintln!($($arg)*); } }
}
#[macro_export]
macro_rules! kdbg {
    ($($v:expr),*) => { if cfg!(debug_assertions) { dbg!($($v),*) } else { ($($v),*) } }
}

pub mod kyoproio {
    use std::{
        io::prelude::*,
        iter::FromIterator,
        marker::PhantomData,
        mem::{self, MaybeUninit},
        str,
    };

    pub trait Input {
        fn bytes(&mut self) -> &[u8];
        fn str(&mut self) -> &str {
            str::from_utf8(self.bytes()).unwrap()
        }
        fn input<T: InputItem>(&mut self) -> T {
            T::input(self)
        }
        fn iter<T: InputItem>(&mut self) -> Iter<T, Self> {
            Iter(self, PhantomData)
        }
        fn collect<T: InputItem, B: FromIterator<T>>(&mut self, n: usize) -> B {
            self.iter().take(n).collect()
        }
        fn map<T: InputItem, U, F: FnMut(T) -> U, B: FromIterator<U>>(
            &mut self,
            n: usize,
            f: F,
        ) -> B {
            self.iter().take(n).map(f).collect()
        }
    }
    impl<I: Input> Input for &mut I {
        fn bytes(&mut self) -> &[u8] {
            (**self).bytes()
        }
    }
    pub struct KInput<R> {
        src: R,
        buf: Vec<u8>,
        pos: usize,
        len: usize,
    }
    impl<R: Read> KInput<R> {
        pub fn new(src: R) -> Self {
            Self {
                src,
                buf: vec![0; 1 << 16],
                pos: 0,
                len: 0,
            }
        }
        fn read(&mut self) -> usize {
            if self.pos > 0 {
                self.buf.copy_within(self.pos..self.len, 0);
                self.len -= self.pos;
                self.pos = 0;
            } else if self.len >= self.buf.len() {
                self.buf.resize(2 * self.buf.len(), 0);
            }
            let n = self.src.read(&mut self.buf[self.len..]).unwrap();
            self.len += n;
            n
        }
    }
    impl<R: Read> Input for KInput<R> {
        fn bytes(&mut self) -> &[u8] {
            loop {
                while let Some(d) = self.buf[self.pos..self.len]
                    .iter()
                    .position(u8::is_ascii_whitespace)
                {
                    let p = self.pos;
                    self.pos += d + 1;
                    if d > 0 {
                        return &self.buf[p..p + d];
                    }
                }
                if self.read() == 0 {
                    return &self.buf[mem::replace(&mut self.pos, self.len)..self.len];
                }
            }
        }
    }
    pub struct Iter<'a, T, I: ?Sized>(&'a mut I, PhantomData<*const T>);
    impl<'a, T: InputItem, I: Input + ?Sized> Iterator for Iter<'a, T, I> {
        type Item = T;
        fn next(&mut self) -> Option<T> {
            Some(self.0.input())
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            (!0, None)
        }
    }
    pub trait InputItem: Sized {
        fn input<I: Input + ?Sized>(src: &mut I) -> Self;
    }
    impl InputItem for Vec<u8> {
        fn input<I: Input + ?Sized>(src: &mut I) -> Self {
            src.bytes().to_owned()
        }
    }
    macro_rules! from_str {
        ($($T:ty)*) => {$(
            impl InputItem for $T {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    src.str().parse::<$T>().unwrap()
                }
            }
        )*}
    }
    from_str!(String char bool f32 f64);
    macro_rules! parse_int {
        ($($I:ty: $U:ty)*) => {$(
            impl InputItem for $I {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    let f = |s: &[u8]| s.iter().fold(0, |x, b| 10 * x + (b & 0xf) as $I);
                    let s = src.bytes();
                    if let Some((&b'-', t)) = s.split_first() { -f(t) } else { f(s) }
                }
            }
            impl InputItem for $U {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    src.bytes().iter().fold(0, |x, b| 10 * x + (b & 0xf) as $U)
                }
            }
        )*}
    }
    parse_int!(isize:usize i8:u8 i16:u16 i32:u32 i64:u64 i128:u128);
    macro_rules! tuple {
        ($H:ident $($T:ident)*) => {
            impl<$H: InputItem, $($T: InputItem),*> InputItem for ($H, $($T),*) {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    ($H::input(src), $($T::input(src)),*)
                }
            }
            tuple!($($T)*);
        };
        () => {}
    }
    tuple!(A B C D E F G);
    macro_rules! array {
        ($($N:literal)*) => {$(
            impl<T: InputItem> InputItem for [T; $N] {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    unsafe {
                        let mut arr: [MaybeUninit<T>; $N] = MaybeUninit::uninit().assume_init();
                        for elem in &mut arr {
                            *elem = MaybeUninit::new(src.input());
                        }
                        mem::transmute_copy(&arr)
                    }
                }
            }
        )*}
    }
    array!(1 2 3 4 5 6 7 8);
}