use std::cmp::*; // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 macro_rules! input { ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes.by_ref().map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } macro_rules! input_inner { ($next:expr) => {}; ($next:expr,) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } macro_rules! read_value { ($next:expr, ( $($t:tt),* )) => { ($(read_value!($next, $t)),*) }; ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, usize1) => (read_value!($next, usize) - 1); ($next:expr, $t:ty) => ($next().parse::<$t>().expect("Parse error")); } /** * Segment Tree. This data structure is useful for fast folding on intervals of an array * whose elements are elements of monoid I. Note that constructing this tree requires the identity * element of I and the operation of I. * Verified by: yukicoder No. 259 (http://yukicoder.me/submissions/100581) * AGC015-E (http://agc015.contest.atcoder.jp/submissions/1461001) * yukicoder No. 833 (https://yukicoder.me/submissions/703521) */ struct SegTree { n: usize, dat: Vec, op: BiOp, e: I, } impl SegTree where BiOp: Fn(I, I) -> I, I: Copy { pub fn new(n_: usize, op: BiOp, e: I) -> Self { let mut n = 1; while n < n_ { n *= 2; } // n is a power of 2 SegTree {n: n, dat: vec![e; 2 * n - 1], op: op, e: e} } /* ary[k] <- v */ pub fn update(&mut self, idx: usize, v: I) { let mut k = idx + self.n - 1; self.dat[k] = v; while k > 0 { k = (k - 1) / 2; self.dat[k] = (self.op)(self.dat[2 * k + 1], self.dat[2 * k + 2]); } } /* [a, b) (note: half-inclusive) * http://proc-cpuinfo.fixstars.com/2017/07/optimize-segment-tree/ */ #[allow(unused)] pub fn query(&self, mut a: usize, mut b: usize) -> I { let mut left = self.e; let mut right = self.e; a += self.n - 1; b += self.n - 1; while a < b { if (a & 1) == 0 { left = (self.op)(left, self.dat[a]); } if (b & 1) == 0 { right = (self.op)(self.dat[b - 1], right); } a = a / 2; b = (b - 1) / 2; } (self.op)(left, right) } } fn main() { input! { _n: usize, m: usize, q: usize, ab: [(usize1, usize1); q], } let mut ab = ab; ab.sort_by_key(|&(a, b)| (a, Reverse(b))); const INF: i64 = 1 << 50; let mut st = SegTree::new(m + 1, max, -INF); st.update(m, 0); for &(_a, b) in ab.iter().rev() { let val = st.query(b + 1, m + 1) + 1; let val = max(val, st.query(b, b + 1)); st.update(b, val); } println!("{}", st.query(0, m + 1)); }