import java.util.*;

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

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