use std::collections::*;
use std::io::Write;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

fn run() {
    input! {
        n: usize,
        e: [(usize1, usize1); n - 1],
    }
    let mut g = vec![vec![]; n];
    for (a, b) in e {
        g[a].push(b);
        g[b].push(a);
    }
    let root = 0;
    let mut topo = vec![root];
    let mut parent = vec![n; n];
    for i in 0..n {
        let v = topo[i];
        for u in g[v].clone() {
            parent[u] = v;
            g[u].retain(|p| *p != v);
            topo.push(u);
        }
    }
    // 子までのmax, 直径
    let mut dp = vec![(0, 0); n];
    for &v in topo.iter().rev() {
        let mut val = (0, 0);
        for &u in g[v].iter() {
            let (a, b) = dp[u];
            val = (val.0.max(a + 1), b.max(val.1).max(val.0 + 1 + a));
        }
        dp[v] = val;
    }
    let under = dp;
    let mut up = vec![(0, 0); n];
    let mut ans = n as i32 - 1;
    for &v in topo.iter() {
        let mut stack = vec![up[v]];
        for (i, &u) in g[v].iter().enumerate() {
            let (a, b) = under[u];
            let val = stack[i];
            stack.push((val.0.max(a + 1), b.max(val.1).max(val.0 + 1 + a)));
        }
        let mut val = (0, 0);
        for (i, &u) in g[v].iter().enumerate().rev() {
            let (a, b) = stack[i];
            let (c, d) = under[u];
            let p = a.max(val.0);
            let q = b.max(val.1).max(val.0 + a);
            ans = ans.min(q.max(d).max((q + 1) / 2 + 1 + (d + 1) / 2));
            up[u] = (p + 1, q.max(p + 1));
            let (a, b) = under[u];
            val = (val.0.max(a + 1), b.max(val.1).max(val.0 + 1 + a));
        }
    }
    println!("{}", ans);
}

fn main() {
    run();
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
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_export]
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)*}
    };
}

#[macro_export]
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, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------