Problem:
Score : 1000 points

Problem Statement

#nck {
width: 30px;
height: auto;
}

Welcome to CODE FESTIVAL 2016!
In order to celebrate this contest, find a string s that satisfies the following conditions:

The length of s is between 1 and 5000, inclusive.

s consists of uppercase letters.

s contains exactly K occurrences of the string "FESTIVAL" as a subsequence.
In other words, there are exactly K tuples of integers (i_0, i_1, ..., i_7) such that 0 ≤ i_0 < i_1 < ... < i_7 ≤ |s|-1 and s[i_0]='F', s[i_1]='E', ..., s[i_7]='L'.

It can be proved that under the given constraints, the solution always exists.
In case there are multiple possible solutions, you can output any.

Constraints

1 ≤ K ≤ 10^{18}

Input

The input is given from Standard Input in the following format:

K

Output

Print a string that satisfies the conditions.

Sample Input 1

7

Sample Output 1

FESSSSSSSTIVAL

Sample Input 2

256

Sample Output 2

FFEESSTTIIVVAALL

Solution in Rust (1.15.1) (judge verdict: Accepted)

const S: usize = 600;
fn main() {
    let (r, w) = (std::io::stdin(), std::io::stdout());
    let mut sc = IO::new(r.lock(), w.lock());

    let mut dp = vec![vec![0; 8]; S];
    for i in 0..dp.len() {
        dp[i][0] = 1;
    }
    for from in 0..dp.len() {
        for to in from..dp.len() {
            for i in 0..7 {
                dp[to][i + 1] += dp[from][i];
            }
        }
    }

    let mut k: usize = sc.read();
    let mut last = vec![0; S];
    for s in (0..S).rev() {
        if k >= dp[s][7] {
            last[s] = k / dp[s][7];
            k %= dp[s][7];
        }
    }
    assert_eq!(k, 0);
    for i in 0..S {
        sc.write("FESTIVA");
        for _ in 0..last[i] {
            sc.write("L");
        }
    }
    sc.write("\n");
}

pub struct IO<R, W: std::io::Write>(R, std::io::BufWriter<W>);

impl<R: std::io::Read, W: std::io::Write> IO<R, W> {
    pub fn new(r: R, w: W) -> IO<R, W> {
        IO(r, std::io::BufWriter::new(w))
    }
    pub fn write<S: std::ops::Deref<Target = str>>(&mut self, s: S) {
        use std::io::Write;
        self.1.write(s.as_bytes()).unwrap();
    }
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .0
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r' && b != b'\t')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }
    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}