import java.util.Scanner;

class Y9011{
    public static void main(String args[]){
        Scanner sc=new Scanner(System.in);
        String s=sc.next();
        int sum=0;
        for(int i=0;i<s.length();i++){
            char ch=s.charAt(i);
            sum+=ch-'0';
        }
        System.out.println(sum);
    }
}