const INF: i32 = 1010101010;

fn main() {
  use std::cmp::max;
  let n: usize = input();
  
  let p = primes(n + 1);
  let m = p.len();

  let mut dp = vec![[-INF; 20001]; m + 1];
  dp[0][0] = 0;

  for i in 0..m {
    for j in 0..n + 1 {
      dp[i + 1][j] = max(dp[i + 1][j], dp[i][j]);
      if j + p[i] <= n {
        dp[i + 1][j + p[i]] = max(dp[i + 1][j + p[i]], dp[i][j] + 1);
      }
    }
  }

  if dp[m][n] >= 0 {
    println!("{}", dp[m][n]);
  } else {
    println!("-1");
  }
}

fn primes(n: usize) -> Vec<usize> {
  let mut res = Vec::new();
  let mut table = vec![true; n];
  for i in 2..n {
    if table[i] {
      res.push(i);
      let mut j = i * 2;
      while j < n {
        table[j] = false;
        j += i;
      }
    }
  }
  res
}

fn input<T: std::str::FromStr>() -> T {
  use std::io::Read;
  let stdin = std::io::stdin();
  let stdin = stdin.bytes();
  let token = stdin
    .skip_while(|x| (*x.as_ref().unwrap() as char).is_whitespace())
    .take_while(|x| !(*x.as_ref().unwrap() as char).is_whitespace())
    .map(|x| x.unwrap())
    .collect();
  let token = String::from_utf8(token).unwrap();
  match token.parse() {
    Ok(x) => x,
    Err(_) => panic!("{}", token),
  }
}