use std::collections::BTreeMap;


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 queries = (0..n).map(|_| {
            let mut ab = String::new();
            std::io::stdin().read_line(&mut ab).ok();
            let ab: Vec<usize> = ab.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
            (ab[0], ab[1])
        })
        .collect::<Vec<_>>();

    let mut lower = 0usize;
    let mut upper = 1e9 as usize;
    while upper > lower {
        let middle = (lower + upper) / 2;
        let mut lcnts = 0usize;
        let mut flg = false;
        for &(a, b) in queries.iter() {
            flg |= a <= middle && middle <= b;
            if a <= middle {
                lcnts += (middle - a + 1).min(b - a + 1);
            }
        }
        if lcnts >= k {
            if flg {
                upper = middle;
            } else {
                upper = middle - 1;
            }
        } else {
            lower = middle + 1;
        }
    }
    println!("{}", upper);
}