In the loop we are decreasing 0 , 9 , 99 ... from n till ( n - i + 1 ) is greater than 0 and sum them to number_of_digits to get the required sum
for i in range ( 1 , n , 10 ) : NEW_LINE INDENT number_of_digits = ( number_of_digits + ( n - i + 1 ) ) ; NEW_LINE DEDENT return number_of_digits ; NEW_LINE