import java.util.*;
class Main {
    public static void main(String[] args) {
	Scanner sc = new Scanner(System.in);
	String s = sc.next();
	int b = 0;
	int r = 0;
	for(int i = 0; i<s.length();i++) {
	    char c = s.charAt(i);
	    if(c=='0') b++;
	    else r++;
	}
	System.out.println((int)Math.min(b,r)*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