import java.util.*;

class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
		char[] a = sc.next().toCharArray();
		int ans=0;
		for (int i=0;i<3;i++){
			if (a[i]=='1'){
            	ans+=1;
            }
        }
        System.out.print(ans);
    }
} import java.util.*; util.* java class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
		char[] a = sc.next().toCharArray();
		int ans=0;
		for (int i=0;i<3;i++){
			if (a[i]=='1'){
            	ans+=1;
            }
        }
        System.out.print(ans);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
		char[] a = sc.next().toCharArray();
		int ans=0;
		for (int i=0;i<3;i++){
			if (a[i]=='1'){
            	ans+=1;
            }
        }
        System.out.print(ans);
    } main {
        Scanner sc = new Scanner(System.in);
		char[] a = sc.next().toCharArray();
		int ans=0;
		for (int i=0;i<3;i++){
			if (a[i]=='1'){
            	ans+=1;
            }
        }
        System.out.print(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) char[] a = sc.next().toCharArray(); a sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc int ans=0; ans 0 for (int i=0;i<3;i++){
			if (a[i]=='1'){
            	ans+=1;
            }
        } int i=0; int i=0; i 0 i<3 i 3 i++ i++ i {
			if (a[i]=='1'){
            	ans+=1;
            }
        } {
			if (a[i]=='1'){
            	ans+=1;
            }
        } if (a[i]=='1'){
            	ans+=1;
            } a[i]=='1' a[i] a i '1' {
            	ans+=1;
            } ans+=1 ans 1 System.out.print(ans) System.out.print System.out System System.out ans String[] args args
import java.util.*;

class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
		char[] a = sc.next().toCharArray();
		int ans=0;
		for (int i=0;i<3;i++){
			if (a[i]=='1'){
            	ans+=1;
            }
        }
        System.out.print(ans);
    }
}