//TODO
fn main() {
    const ALPHABETS: &str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

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

    let mut powval: u32 = 1;
    while n >= 26usize.pow(powval) {
        n -= 26usize.pow(powval);
        powval += 1;
    }
    let mut result = String::new();
    (0..powval).rev().for_each(|i| {
        let divval: usize = 26usize.pow(i);
        result.push(ALPHABETS.chars().nth(n / divval).unwrap());
        n %= divval;
    });
    println!("{}", result);
}