import java.util.Scanner;

class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String str = sc.nextLine();
    int[] a = new int[3];
    int count = 0;
    for(int i=0;i<3;i++){
      a[i] = Integer.valueOf(str.substring(i,i+1));
    }
    for(int j : a){
      if(j == 1) count++;
    }
    System.out.print(count);
  }
}
/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