import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        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);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = Integer.parseInt(sc.next()); a Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int count = 0; count 0 for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        } int i=0; int i=0; i 0 i<3 i 3 i++ i++ i {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        } {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        } if ((a % 10) == 1) {
                count++;
            } (a % 10) == 1 (a % 10) a 10 1 {
                count++;
            } count++ count a /= 10 a 10 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);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        System.out.println(count);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = Integer.parseInt(sc.next());
        int count = 0;
        for(int i=0; i<3; i++) {
            if ((a % 10) == 1) {
                count++;
            }
            a /= 10;
        }
        System.out.println(count);
    }
}
