import java.util.Scanner;

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

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