import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main {

    private void solve() {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        char[] chars = S.toCharArray();
        int zeroNum = 0;
        int oneNum = 0;
        for (char ch : chars) {
            if (ch == '0') {
                zeroNum++;
            }
            else {
                oneNum++;
            }
        }
        int min = Math.min(zeroNum, oneNum);
        int ans = min * 2;
        System.out.print(ans);
    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz