import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  } main {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] spaces = sc.nextLine().split(""); spaces sc.nextLine().split("") sc.nextLine().split sc.nextLine() sc.nextLine sc "" int count = 0; count 0 for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    } String space spaces {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    } {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    } if (Integer.parseInt(space) == 1) {
        count++;
      } Integer.parseInt(space) == 1 Integer.parseInt(space) Integer.parseInt Integer space 1 {
        count++;
      } count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String[] spaces = sc.nextLine().split("");
    int count = 0;

    for (String space: spaces) {
      if (Integer.parseInt(space) == 1) {
        count++;
      }
    }

    System.out.println(count);
  }
}
