import java.util.*;
class Main 
{
	public static void main(String[]args)
	{
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		int count=0;
		for(int i=0;i<str.length();i++)
		{
			if(str.charAt(i)=='1')
				count++;
		}
		System.out.println(count);
	}
} import java.util.*; util.* java class Main 
{
	public static void main(String[]args)
	{
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		int count=0;
		for(int i=0;i<str.length();i++)
		{
			if(str.charAt(i)=='1')
				count++;
		}
		System.out.println(count);
	}
} Main public static void main(String[]args)
	{
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		int count=0;
		for(int i=0;i<str.length();i++)
		{
			if(str.charAt(i)=='1')
				count++;
		}
		System.out.println(count);
	} main {
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		int count=0;
		for(int i=0;i<str.length();i++)
		{
			if(str.charAt(i)=='1')
				count++;
		}
		System.out.println(count);
	} Scanner sc=new Scanner(System.in); sc new Scanner(System.in) String str=sc.nextLine(); str sc.nextLine() sc.nextLine sc int count=0; count 0 for(int i=0;i<str.length();i++)
		{
			if(str.charAt(i)=='1')
				count++;
		} int i=0; int i=0; i 0 i<str.length() i str.length() str.length str i++ i++ i {
			if(str.charAt(i)=='1')
				count++;
		} {
			if(str.charAt(i)=='1')
				count++;
		} if(str.charAt(i)=='1')
				count++; str.charAt(i)=='1' str.charAt(i) str.charAt str i '1' count++ count System.out.println(count) System.out.println System.out System System.out count String[]args args
import java.util.*;
class Main 
{
	public static void main(String[]args)
	{
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		int count=0;
		for(int i=0;i<str.length();i++)
		{
			if(str.charAt(i)=='1')
				count++;
		}
		System.out.println(count);
	}
}