import java.io.*;
 
public class Main{
  public static void main(String[] args)throws IOException{
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    
    String input = br.readLine();
    int zero = 0;
    for(int i = 0; i<input.length(); i++){
      if(input.indexOf('1',i) == i){
        zero++;
      }
    }
	System.out.println(zero);
  }
}

/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