import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        }
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        }
    }
} Main public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        }
    } main {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        }
    } try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        } {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        } Scanner in = new Scanner(System.in) Scanner in = new Scanner(System.in) new Scanner(System.in) String s = in.next(); s in.next() in.next in int count = 0; count 0 for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
                if (s.charAt(i) == '1') {
                    count++;
                }
            } {
                if (s.charAt(i) == '1') {
                    count++;
                }
            } if (s.charAt(i) == '1') {
                    count++;
                } s.charAt(i) == '1' s.charAt(i) s.charAt s i '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) {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        }
    }
} public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

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

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            String s = in.next();

            int count = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '1') {
                    count++;
                }
            }

            System.out.println(count);
        }
    }
}
