import java.util.Scanner;

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

		System.out.println(count);
    }

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

		System.out.println(count);
    } main {
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		int count = 0;
		for(int i = 0;i < 3;i++) {
		    if(s[i] - '0' == 1) count++; 
		}

		System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) char[] s = sc.next().toCharArray(); s sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc int count = 0; count 0 for(int i = 0;i < 3;i++) {
		    if(s[i] - '0' == 1) count++; 
		} int i = 0; int i = 0; i 0 i < 3 i 3 i++ i++ i {
		    if(s[i] - '0' == 1) count++; 
		} {
		    if(s[i] - '0' == 1) count++; 
		} if(s[i] - '0' == 1) count++; s[i] - '0' == 1 s[i] - '0' s[i] s i '0' 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);
		char[] s = sc.next().toCharArray();
		int count = 0;
		for(int i = 0;i < 3;i++) {
		    if(s[i] - '0' == 1) count++; 
		}

		System.out.println(count);
    }

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

		System.out.println(count);
    }

} Main
import java.util.Scanner;

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

		System.out.println(count);
    }

}