Problem:
Score : 300 points

Problem Statement

1000000000000001 dogs suddenly appeared under the roof of Roger's house, all of which he decided to keep. The dogs had been numbered 1 through 1000000000000001, but he gave them new names, as follows:

the dogs numbered 1,2,\cdots,26 were respectively given the names a, b, ..., z;

the dogs numbered 27,28,29,\cdots,701,702 were respectively given the names aa, ab, ac, ..., zy, zz;

the dogs numbered 703,704,705,\cdots,18277,18278 were respectively given the names aaa, aab, aac, ..., zzy, zzz;

the dogs numbered 18279,18280,18281,\cdots,475253,475254 were respectively given the names aaaa, aaab, aaac, ..., zzzy, zzzz;

the dogs numbered 475255,475256,\cdots were respectively given the names aaaaa, aaaab, ...;

and so on.

To sum it up, the dogs numbered 1, 2, \cdots were respectively given the following names:

a, b, ..., z, aa, ab, ..., az, ba, bb, ..., bz, ..., za, zb, ..., zz, aaa, aab, ..., aaz, aba, abb, ..., abz, ..., zzz, aaaa, ...

Now, Roger asks you:

"What is the name for the dog numbered N?"

Constraints

N is an integer.

1 \leq N \leq 1000000000000001

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer to Roger's question as a string consisting of lowercase English letters.

Sample Input 1

2

Sample Output 1

b

Sample Input 2

27

Sample Output 2

aa

Sample Input 3

123456789

Sample Output 3

jjddja

Solution in Rust (1.42.0) (judge verdict: Accepted)

fn main() {
    let n: i64 = read();
    println!("{}", solve(n));
}

fn read<T: std::str::FromStr>() -> T {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).ok();
    buf.trim().parse().ok().unwrap()
}

fn solve(n: i64) -> String {
    // 要するに26進数
    let mut s = "".to_string();
    let mut i = n;
    while {
        s = ((b'a' + ((i - 1) % 26) as u8) as char).to_string() + &s;

        i = (i - 1) / 26;
        i > 0
    } {}

    s
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_solve_1() {
        assert_eq!("b".to_string(), solve(2));
    }

    #[test]
    fn test_solve_2() {
        assert_eq!("aa".to_string(), solve(27));
    }

    #[test]
    fn test_solve_3() {
        assert_eq!("jjddja".to_string(), solve(123456789));
    }

    #[test]
    fn test_solve_4() {
        assert_eq!("zz".to_string(), solve(702));
    }

    #[test]
    fn test_solve_5() {
        assert_eq!("aaab".to_string(), solve(18280));
    }
}