#[macro_use]
mod input_mcr {
    // ref: tanakh <https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8>
    // diff: using Parser
    #[macro_export(local_inner_macros)]
    macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut parser = Parser::from_str($s);
        input_inner!{parser, $($r)*}
    };
    (parser = $parser:ident, $($r:tt)*) => {
        input_inner!{$parser, $($r)*}
    };
    (new_stdin_parser = $parser:ident, $($r:tt)*) => {
        let stdin = std::io::stdin();
        let reader = std::io::BufReader::new(stdin.lock());
        let mut $parser = Parser::new(reader);
        input_inner!{$parser, $($r)*}
    };
    ($($r:tt)*) => {
        input!{new_stdin_parser = parser, $($r)*}
    };
}

    #[macro_export(local_inner_macros)]
    macro_rules! input_inner {
    ($parser:ident) => {};
    ($parser:ident, ) => {};
    ($parser:ident, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($parser, $t);
        input_inner!{$parser $($r)*}
    };
}

    #[macro_export(local_inner_macros)]
    macro_rules! read_value {
    ($parser:ident, ( $($t:tt),* )) => {
        ( $(read_value!($parser, $t)),* )
    };
    ($parser:ident, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($parser, $t)).collect::<Vec<_>>()
    };
    ($parser:ident, chars) => {
        read_value!($parser, String).chars().collect::<Vec<char>>()
    };
    ($parser:ident, char_) => {
        read_value!($parser, String).chars().collect::<Vec<char>>()[0]
    };
    ($parser:ident, usize1) => {
        read_value!($parser, usize) - 1
    };
    ($parser:ident, i64_) => {
        $parser.fast_i64()
    };
    ($parser:ident, usize_) => {
        $parser.fast_i64() as usize
    };
    ($parser:ident, usize1_) => {
        ($parser.fast_i64() - 1) as usize
    };
    ($parser:ident, $t:ty) => {
        $parser.next::<$t>().expect("Parse error")
    };
}

    use std::io;
    use std::io::BufRead;
    use std::str;

    // ref: tatsuya6502 <https://qiita.com/tatsuya6502/items/cd448486f7ef7b5b8c7e>
    // ref: wariuni <https://qiita.com/tatsuya6502/items/cd448486f7ef7b5b8c7e#comment-7040a5ae96305e884eb9>
    // diff: using std::io::BufRead::fill_buf()
    pub struct Parser<R> {
        pub reader: R,
        buf: Vec<u8>,
        pos: usize,
    }

    impl Parser<io::Empty> {
        pub fn from_str(s: &str) -> Parser<io::Empty> {
            Parser {
                reader: io::empty(),
                buf: s.as_bytes().to_vec(),
                pos: 0,
            }
        }
    }

    impl<R: BufRead> Parser<R> {
        pub fn new(reader: R) -> Parser<R> {
            Parser {
                reader: reader,
                buf: vec![],
                pos: 0,
            }
        }
        pub fn update_buf(&mut self) {
            self.buf.clear();
            self.pos = 0;
            loop {
                let (len, complete) = {
                    let buf2 = self.reader.fill_buf().unwrap();
                    self.buf.extend_from_slice(buf2);
                    let len = buf2.len();
                    (len, buf2[len - 1] <= 0x20)
                };
                self.reader.consume(len);
                if complete {
                    break;
                }
            }
        }
        pub fn next<T: str::FromStr>(&mut self) -> Result<T, T::Err> {
            loop {
                let mut begin = self.pos;
                while begin < self.buf.len() && (self.buf[begin] <= 0x20) {
                    begin += 1;
                }
                let mut end = begin;
                while end < self.buf.len() && (self.buf[end] > 0x20) {
                    end += 1;
                }
                if begin != self.buf.len() {
                    self.pos = end;
                    return unsafe { str::from_utf8_unchecked(&self.buf[begin..end]) }.parse::<T>();
                } else {
                    self.update_buf();
                }
            }
        }
        pub fn fast_i64(&mut self) -> i64 {
            loop {
                let mut begin = self.pos;
                while begin < self.buf.len() && (self.buf[begin] <= 0x20) {
                    begin += 1;
                }
                if begin == self.buf.len() {
                    self.update_buf();
                    continue;
                }
                let mut res = 0;
                let (is_positive, mut end) = match self.buf[begin] {
                    b'+' => (true, begin + 1),
                    b'-' => (false, begin + 1),
                    _ => (true, begin),
                };
                while end < self.buf.len() && (self.buf[end] > 0x20) {
                    res = res * 10 + (self.buf[end] as i64 - '0' as i64);
                    end += 1;
                }
                if begin != self.buf.len() {
                    self.pos = end;
                    return if is_positive { res } else { -res };
                } else {
                    self.update_buf();
                }
            }
        }
    }
}

use input_mcr::*;
use std::cmp::*;
use std::collections::BTreeMap;

fn f(xs: &Vec<(i64, i64)>) -> i64 {
    let n = xs.len();
    let mut res = 0;
    for iter in 0..2 {
        let mut xs = xs.clone();
        if iter == 0 {
            xs.sort();
        } else {
            let mut ys = vec![];
            for &(l, r) in &xs {
                ys.push((l, -r));
            }
            ys.sort();
            xs.clear();
            for &(l, r) in &ys {
                xs.push((l, -r));
            }
            /*
            xs.sort_by(|&x,&y| {
                if x.0 != y.0 {
                    x.0.cmp(&y.0)
                }
                else {
                    y.0.cmp(&x.0)
                }
            })*/
        }
        // eprintln!("iter = {}, xs = {:?}", iter, xs);
        let n = xs.len();
        let inf = 1i64 << 50;
        let mut lower_left_max = vec![inf; n];
        let mut t = 0;
        for i in 0..n {
            t = max(t, xs[i].0);
            lower_left_max[i] = t;
        }
        let mut lower_right_min = vec![0; n];
        let mut t = inf;
        for i in 0..n {
            t = min(t, xs[i].1);
            lower_right_min[i] = t;
        }
        let mut upper_left_max = vec![inf; n];
        let mut t = 0;
        for i in (0..n).rev() {
            t = max(t, xs[i].0);
            upper_left_max[i] = t;
        }
        let mut upper_right_min = vec![0; n];
        let mut t = inf;
        for i in (0..n).rev() {
            t = min(t, xs[i].1);
            upper_right_min[i] = t;
        }
        for i in 0..n - 1 {
            let t = max(0, lower_right_min[i] - lower_left_max[i] + 1);
            let u = max(0, upper_right_min[i + 1] - upper_left_max[i + 1] + 1);
            res = max(res, t + u);
        }
        for i in 0..n {
            let t = max(0, xs[i].1 - xs[i].0 + 1);
            let mut right_min = inf;
            if i > 0 {
                right_min = min(right_min, lower_right_min[i - 1]);
            }
            if i < n - 1 {
                right_min = min(right_min, upper_right_min[i + 1]);
            }
            let mut left_max = 0;
            if i > 0 {
                left_max = max(left_max, lower_left_max[i - 1]);
            }
            if i < n - 1 {
                left_max = max(left_max, upper_left_max[i + 1]);
            }
            res = max(res, t + max(0, right_min - left_max + 1));
        }
    }
    res
}

fn g(xs: &Vec<(i64, i64)>) -> i64 {
    let n = xs.len();
    let inf = 1i64 << 50;
    let mut res = 0;
    for i in 1..(1 << n - 1) {
        let mut left_max = [0, 0];
        let mut right_min = [inf, inf];
        for k in 0..n {
            if i & (1 << k) == 0 {
                left_max[0] = max(left_max[0], xs[k].0);
                right_min[0] = min(right_min[0], xs[k].1);
            } else {
                left_max[1] = max(left_max[1], xs[k].0);
                right_min[1] = min(right_min[1], xs[k].1);
            }
        }
        let s = max(0, right_min[0] - left_max[0] + 1);
        let t = max(0, right_min[1] - left_max[1] + 1);
        res = max(res, s + t);
    }
    res
}

fn gen_all_range(l: i64, r: i64) -> Vec<(i64, i64)> {
    let mut res = vec![];
    for i in l..r {
        for k in i + 1..r {
            res.push((i, k));
        }
    }
    res
}

fn main() {
    /*
    for &r1 in &gen_all_range(0,5) {
        for &r2 in &gen_all_range(0,5) {
            for &r3 in &gen_all_range(0,5) {
                for &r4 in &gen_all_range(0,5) {
                    let ts = vec![r1, r2, r3, r4];
                    assert_eq!(f(&ts), g(&ts), "ts = {:?}", ts);
                }
            }
        }
    }
    */
    input! {
        n: usize,
        xs: [(i64,i64); n],
    }
    let res = f(&xs);
    println!("{}", res);
}



Measured memory_bytes: 14588