import java.util.Scanner;

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

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