use proconio::input;

fn main () {
    input! {
        n: u128,
    }
    let prime: Vec<u128> = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47].to_vec();
    let ans = prime.iter().enumerate()
        .fold((1, 1), |(index, num), (i, &p)| {
            if num > n {
                (index, num)
            }
            else if num*p > n {
                (i, num*p)
            }
            else {
                (index, num*p)
            }
        });
    if ans.1 < n {
        println!("15");
    }
    else {
        println!("{}", ans.0);
    }
}