#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>


int main() {
  system("cls");
  //INPUT - @STUDENT:ADD YOUR CODE FOR INPUT HERE:
	int a, i, sum;
	int b[15], count;
	
	scanf("%d", &a);
	
	count = 0; i = 0;
	while (a>0) {
		b[i] = a%10;
		count++;
		a /= 10;
	}
	
	sum = 0;
	for (int i = count-1; i>=0; i-=2) {
		sum +=i;
	}
  

  // Fixed Do not edit anything here.
  printf("\nOUTPUT:\n");
  //@STUDENT: WRITE YOUR OUTPUT HERE:
	printf("%d",sum);


  
  //--FIXED PART - DO NOT EDIT ANY THINGS HERE
  printf("\n");
  system ("pause");
  return(0);
}