Function to return the number of positive integers less than or equal to N that have odd number of digits
def odd_digits ( n ) : NEW_LINE INDENT if ( n < 10 ) : NEW_LINE INDENT return n ; NEW_LINE DEDENT elif ( n / 10 < 10 ) : NEW_LINE INDENT return 9 ; NEW_LINE DEDENT elif ( n / 100 < 10 ) : NEW_LINE INDENT return 9 + n - 99 ; NEW_LINE DEDENT elif ( n / 1000 < 10 ) : NEW_LINE INDENT return 9 + 900 ; NEW_LINE DEDENT elif ( n / 10000 < 10 ) : NEW_LINE INDENT return 909 + n - 9999 ; NEW_LINE DEDENT else : NEW_LINE INDENT return 90909 ; NEW_LINE DEDENT DEDENT