#[allow(unused_imports)] use std::cmp::{max, min, Ordering}; #[allow(unused_imports)] use std::collections::{HashMap, HashSet, BinaryHeap, VecDeque}; #[allow(unused_imports)] use std::iter::FromIterator; #[allow(unused_imports)] use std::io::stdin; mod util { use std::io::stdin; use std::str::FromStr; use std::fmt::Debug; #[allow(dead_code)] pub fn line() -> String { let mut line: String = String::new(); stdin().read_line(&mut line).unwrap(); line.trim().to_string() } #[allow(dead_code)] pub fn gets() -> Vec where ::Err: Debug, { let mut line: String = String::new(); stdin().read_line(&mut line).unwrap(); line.split_whitespace() .map(|t| t.parse().unwrap()) .collect() } } #[allow(unused_macros)] macro_rules! get { ($t:ty) => { { let mut line: String = String::new(); stdin().read_line(&mut line).unwrap(); line.trim().parse::<$t>().unwrap() } }; ($($t:ty),*) => { { let mut line: String = String::new(); stdin().read_line(&mut line).unwrap(); let mut iter = line.split_whitespace(); ( $(iter.next().unwrap().parse::<$t>().unwrap(),)* ) } }; ($t:ty; $n:expr) => { (0..$n).map(|_| get!($t) ).collect::>() }; ($($t:ty),*; $n:expr) => { (0..$n).map(|_| get!($($t),*) ).collect::>() }; ($t:ty ;;) => { { let mut line: String = String::new(); stdin().read_line(&mut line).unwrap(); line.split_whitespace() .map(|t| t.parse::<$t>().unwrap()) .collect::>() } }; } #[allow(unused_macros)] macro_rules! debug { ($($a:expr),*) => { println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*); } } struct SEG T> { n: usize, buf: Vec, reducer: F, } impl T> SEG { fn new(n: usize, zero: &T, f: F) -> SEG { let n = (1..) .map(|i| 2usize.pow(i as u32)) .find(|&x| x > n) .unwrap(); SEG { n: n, buf: vec![zero.clone(); 2 * n], reducer: f, } } fn update(&mut self, k: usize, a: T) { let mut k = k + self.n - 1; self.buf[k] = a; while k > 0 { k = (k - 1) / 2; self.buf[k] = (self.reducer)(&self.buf[k * 2 + 1], &self.buf[k * 2 + 2]); } } fn add(&mut self, k: usize, a: &T) { let mut k = k + self.n - 1; self.buf[k] = (self.reducer)(&self.buf[k], a); while k > 0 { k = (k - 1) / 2; self.buf[k] = (self.reducer)(&self.buf[k * 2 + 1], &self.buf[k * 2 + 2]); } } fn q(&self, a: usize, b: usize, k: usize, l: usize, r: usize) -> Option { if r <= a || b <= l { return None; } if a <= l && r <= b { Some(self.buf[k].clone()) } else { let vl = self.q(a, b, k * 2 + 1, l, (l + r) / 2); let vr = self.q(a, b, k * 2 + 2, (l + r) / 2, r); match (vl, vr) { (Some(l), Some(r)) => Some((self.reducer)(&l, &r)), (Some(l), None) => Some(l), (None, Some(r)) => Some(r), _ => None, } } } fn query(&self, a: usize, b: usize) -> T { self.q(a, b, 0, 0, self.n).unwrap() } } fn main() { let n = get!(usize); let a = get!(usize;;); let mut index = vec![0; n]; for (i, &x) in a.iter().enumerate() { index[x - 1] = i; } let mut seg = SEG::new(n + 1, &0, |&a, &b| a + b); let mut ans = 0; for (k, &i) in index.iter().rev().enumerate() { if seg.query(i, n) != k { ans += 1; } seg.update(i, 1); } println!("{}", ans); }