import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        main.solve();
    }
    public void solve() {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    }
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        main.solve();
    }
    public void solve() {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    }
} Main public static void main(String[] args) {
        Main main = new Main();
        main.solve();
    } main {
        Main main = new Main();
        main.solve();
    } Main main = new Main(); main new Main() main.solve() main.solve main String[] args args public void solve() {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    } solve {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    } Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in))); scan new Scanner(new BufferedReader(new InputStreamReader(System.in))) String s = scan.next(); s scan.next() scan.next scan int answer = 0; answer 0 for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        } char x s.toCharArray() s.toCharArray s {
            if (x == '1') {
                answer += 1;
            }
        } {
            if (x == '1') {
                answer += 1;
            }
        } if (x == '1') {
                answer += 1;
            } x == '1' x '1' {
                answer += 1;
            } answer += 1 answer 1 System.out.println(answer) System.out.println System.out System System.out answer public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        main.solve();
    }
    public void solve() {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    }
} public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        main.solve();
    }
    public void solve() {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    }
} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        main.solve();
    }
    public void solve() {
        Scanner scan = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        String s = scan.next();
        int answer = 0;
        for (char x : s.toCharArray()) {
            if (x == '1') {
                answer += 1;
            }
        }
        System.out.println(answer);
    }
}
