import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
    
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        int cnt0 = 0;
        int cnt1 = 0;
        for(int i = 0; i < S.length(); i++){
            if( S.charAt(i) == '0' ){
                cnt0++;
            } else {
                cnt1++;
            }
        }
        
        System.out.println( Math.min(cnt0, cnt1) * 2 );
        
    }
}

/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