use std::cmp::max;

fn primes(n: usize) -> Vec<usize> {
    let mut flgs: Vec<bool> = vec![true; n+1];
    flgs[0] = false;
    flgs[1] = false;
    let limit: usize = (n as f64).sqrt().ceil() as usize + 1;
    for i in 0..limit {
        if !flgs[i] { continue; }
        for j in i..=n/i {
            flgs[j*i] = false;
        }
    }
    flgs.iter().enumerate()
        .filter(|&pair| *pair.1)
        .map(|pair| pair.0)
        .collect()
}

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    if n == 1 {
        println!("-1");
        return;
    }

    let primes: Vec<usize> = primes(n);
    let mut dp: Vec<usize> = vec![0; n+1];
    for &p in primes.iter() {
        for i in (0..=n-p).rev() {
            if dp[i] > 0 && i + p <= n {
                dp[i + p] = max(dp[i] + 1, dp[i+p]);
            }
        }
        dp[p] = max(dp[p], 1);
    }
    println!("{}", if dp[n] == 0 { -1 } else { dp[n] as isize });
}