import java.util.*;

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

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    char[] s = sc.next().toCharArray();
    
    int ans = 0;
    for (char c : s) {
      if (c == '1') {
        ans++;
      }
    }
    
    System.out.println(ans);
  }
}