fn get_primes(max: usize) -> Vec<usize> {
    let mut is_prime = vec![true; max + 1];
    is_prime[0] = false;
    is_prime[1] = false;

    for n in 2..=max {
        if !is_prime[n] {
            continue;
        }
        if n * n > max {
            break;
        }
        for i in ((n * n)..=max).step_by(n) {
            is_prime[i] = false;
        }
    }

    (0..=max).filter(|&n| is_prime[n]).collect()
}

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();

    let primes = get_primes(n);
    let mut dp = vec![None; n + 1];
    dp[0] = Some(0);

    for &p in &primes {
        for i in (p..=n).rev() {
            if let Some(k) = dp[i - p] {
                dp[i] = Some(dp[i].unwrap_or(0).max(k + 1));
            }
        }
    }

    dp[n].map_or_else(|| println!("-1"), |k| println!("{k}"));
}