// https://atcoder.jp/contests/abc081/tasks/abc081_a

import java.util.Scanner;

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

        String s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);

        String s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int count = 0; count 0 for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        } char ch s.toCharArray() s.toCharArray s {
           if (ch == '1') count++;
        } {
           if (ch == '1') count++;
        } if (ch == '1') count++; ch == '1' ch '1' 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 s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    }
} Main
// https://atcoder.jp/contests/abc081/tasks/abc081_a

import java.util.Scanner;

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

        String s = sc.next();

        int count = 0;
        for(char ch : s.toCharArray()) {
           if (ch == '1') count++;
        }
        System.out.println(count);
    }
}