import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String str = sc.next();
    
    int cnt = 0;
    
    for(int i=0;i<str.length();i++) {
      if(str.substring(i, i+1).equals("1")) {
        cnt += 1;
      }
    }
    System.out.println(cnt);
  }
}
/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