Problem:
Score : 200 points

Problem Statement

There are N + 1 squares arranged in a row, numbered 0, 1, ..., N from left to right.

Initially, you are in Square X.
You can freely travel between adjacent squares. Your goal is to reach Square 0 or Square N.
However, for each i = 1, 2, ..., M, there is a toll gate in Square A_i, and traveling to Square A_i incurs a cost of 1.
It is guaranteed that there is no toll gate in Square 0, Square X and Square N.

Find the minimum cost incurred before reaching the goal.

Constraints

1 \leq N \leq 100

1 \leq M \leq 100

1 \leq X \leq N - 1

1 \leq A_1 < A_2 < ... < A_M \leq N

A_i \neq X

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N M X
A_1 A_2 ... A_M

Output

Print the minimum cost incurred before reaching the goal.

Sample Input 1

5 3 3
1 2 4

Sample Output 1

1

The optimal solution is as follows:

First, travel from Square 3 to Square 4. Here, there is a toll gate in Square 4, so the cost of 1 is incurred.

Then, travel from Square 4 to Square 5. This time, no cost is incurred.

Now, we are in Square 5 and we have reached the goal.

In this case, the total cost incurred is 1.

Sample Input 2

7 3 2
4 5 6

Sample Output 2

0

We may be able to reach the goal at no cost.

Sample Input 3

10 7 5
1 2 3 4 6 8 9

Sample Output 3

3

Solution in Rust (1.15.1) (judge verdict: Accepted)

#[allow(unused_imports)]
use std::cmp::{max, min, Ordering};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Read, StdoutLock, Write};
#[allow(unused_imports)]
use std::iter::FromIterator;
#[allow(unused_imports)]
use std::str::FromStr;

// toll-gates.rs --- Toll Gates
// author: Seong Yong-ju <sei40kr@gmail.com>

#[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!($t)
    ).collect::<Vec<_>>()
  };
  ($($t:ty),*; $n:expr) => {
    (0..$n).map(|_|
                get!($($t),*)
    ).collect::<Vec<_>>()
  };
  ($t:ty ;;) => {
    {
      let mut line: String = String::new();
      stdin().read_line(&mut line).unwrap();
      line.split_whitespace()
        .map(|t| t.parse::<$t>().unwrap())
        .collect::<Vec<_>>()
    }
  };
  ($t:ty ;; $n:expr) => {
    (0..$n).map(|_| get!($t ;;)).collect::<Vec<_>>()
  };
}

#[allow(unused_macros)]
macro_rules! debug {
  ($($a:expr),*) => {
    println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
  }
}

#[allow(dead_code)]
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("Failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("Failed to parse token")
}

#[allow(dead_code)]
fn with_bufwriter<F: FnOnce(BufWriter<StdoutLock>) -> ()>(f: F) {
    let out = stdout();
    let writer = BufWriter::new(out.lock());
    f(writer);
}

fn main() {
    let (_n, m, x) = get!(usize, usize, usize);
    let ys = (0..m).map(|mut _i| read::<usize>()).collect::<Vec<_>>();

    let ans =
        {
            let (m1, m2) = ys.into_iter().fold((0, 0), |(m1, m2), y| {
                if y < x {
                    (m1 + 1, m2)
                } else {
                    (m1, m2 + 1)
                }
            });

            min(m1, m2)
        };

    with_bufwriter(|mut out| writeln!(out, "{}", ans).unwrap());
}