import java.util.Scanner;

/**
   Counts the number of digits with value 7 in the decimal
   representation of the integer n
*/
public class CountSevens
{
   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);
      int n = in.nextInt();
      int count = 0;
      String str = Integer.toString(n);
      for(int i = 0; i < str.length(); i++)
      {
         if(str.charAt(i) == '7'){count++;}
      }

      System.out.println(count);
   }
}