import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    } main {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] n = sc.next().split(""); n sc.next().split("") sc.next().split sc.next() sc.next sc "" int cnt = 0; cnt 0 for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        } String tmp n {
            if (tmp.equals("1")) cnt++;
        } {
            if (tmp.equals("1")) cnt++;
        } if (tmp.equals("1")) cnt++; tmp.equals("1") tmp.equals tmp "1" cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String[] n = sc.next().split("");
        int cnt = 0;
        for (String tmp : n) {
            if (tmp.equals("1")) cnt++;
        }
        System.out.println(cnt);
    }
}
