use std::io::*;
use std::str::FromStr;
/*
const LOW_CASE_ALPHABET: [char; 26] = [
    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
    't', 'u', 'v', 'w', 'x', 'y', 'z',
];
*/

fn main() {
    let s: Vec<char> = read_array();
    let mut tmp = 0;
    for _i in &s{
        if *_i == 'a'{
            tmp += 1;
        }
    }

    for _i in 0..=tmp{
        print!("a");
    }
}

/*
pub fn perfect(value_1: usize) -> usize {
    let mut perfect_number = Vec::new();
    let mut tmp_1 = 0;
    for _i in 2..=value_1 {
        let mut tmp = 0;
        for _j in 1..=((_i as f64).powf(0.5)) as usize {
            if _i % _j == 0 {
                if _j * _j == _i {
                    tmp += _j;
                } else {
                    tmp += _j + (_i / _j);
                }
            }
        }
        tmp -= _i;

        if tmp == _i {
            perfect_number.push(_i);
        }
    }

    for _i in &perfect_number{
        if tmp_1 == perfect_number.len() - 1{
            break;
        }
        println!("{}", _i);
        tmp_1 += 1;
    }

    perfect_number[perfect_number.len() - 1]
}
*/

/*
pub fn prime_number(value_1: usize, value_2: usize) -> usize {
    let mut primary = Vec::new();
    primary.push(2);

    for _i in 2..=value_1 {
        let mut flag = 0;
        for _j in &primary {
            if _i % _j == 0 {
                flag = 1;
                break;
            }
        }
        if flag == 0 {
            primary.push(_i);
        }
        if primary.len() == value_2 {
            return primary[primary.len() - 1];
        }
    }

    0
}
*/

/*
pub fn ctoi(c: char) -> isize {
    c as isize - '0' as isize
}
*/

pub fn stoi(c: String) -> isize {
    c.parse::<isize>().unwrap()
}

/*
pub fn find_char(sentence: Vec<char>, target: char, start: isize) -> isize {
    for _i in start as usize..sentence.len() {
        if sentence[_i] == target {
            return _i as isize;
        }
    }
    -1
}
*/

/*
pub fn hex_to_binary_2(hex_string: String, x: u32) -> Option<String> {
    match i64::from_str_radix(&hex_string, x) {
        Ok(decimal) => Some(format!("{}", decimal)),
        Err(_) => None,
    }
}
*/

/*
pub fn hex_to_binary(hex_string: &str, x: u32) -> Option<String> {
    match i64::from_str_radix(hex_string, x) {
        Ok(decimal) => Some(format!("{}", decimal)),
        Err(_) => None,
    }
}
*/

/*
pub fn my_floor(x: f64) -> f64 {
    (x * 1000.0).floor() / 1000.0
}
*/

/*
pub fn upper_lower(x: char) -> char {
    let result: char;

    if x.is_uppercase() {
        result = x.to_ascii_lowercase();
    } else if x.is_lowercase() {
        result = x.to_ascii_uppercase();
    } else {
        result = x;
    }

    result
}
*/

/*
pub fn maxf_2(x: f64, y: f64) -> f64 {
    if x >= y {
        x
    } else {
        y
    }
}
*/

/*
pub fn max_2(x: isize, y: isize) -> isize {
    if x >= y {
        x
    } else {
        y
    }
}
*/

/*
pub fn min_2(x: isize, y: isize) -> isize {
    if x >= y {
        y
    } else {
        x
    }
}
*/

/*
pub fn max_3(x: isize, y: isize, z: isize) -> isize {
    if (x >= y && y >= z) || (x >= z && z >= y){
        x
    } else if (y >= x && x >= z) || (y >= z && z >= x) {
        y
    } else {
        z
    }
}
*/

/*
pub fn max_u_3(x: usize, y: usize, z: usize) -> usize {
    if (x >= y && y >= z) || (x >= z && z >= y){
        x
    } else if (y >= x && x >= z) || (y >= z && z >= x) {
        y
    } else {
        z
    }
}
*/

/*
pub fn min_3(x: isize, y: isize, z: isize) -> isize {
    if (x <= y && y <= z) || (x <= z && z <= y){
        x
    } else if (y <= x && x <= z) || (y <= z && z <= x) {
        y
    } else {
        z
    }
}
*/

/*
pub fn min_u_3(x: usize, y: usize, z: usize) -> usize {
    if (x <= y && y <= z) || (x <= z && z <= y){
        x
    } else if (y <= x && x <= z) || (y <= z && z <= x) {
        y
    } else {
        z
    }
}
*/

pub fn read_text() -> String {
    let mut word = String::new();
    std::io::stdin().read_line(&mut word).ok();
    let answer = word.trim().to_string();

    answer
}

pub fn read_array() -> Vec<char> {
    let array: String = read();
    let chars: Vec<char> = array.trim().chars().collect::<Vec<char>>();
    chars
}

pub fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

pub fn read_line<T: FromStr>() -> String {
    let stdin = stdin();
    let stdin = stdin.lock();
    stdin
        .lines()
        .next()
        .expect("No line in the input")
        .expect("Failed to read line")
}