Problems
Two identical digits
Two identical digits
Four-digit number is given. Determine whether it contains exactly two different digits, each of these digits must occur twice. For example, the numbers 2727 and 6677 satisfy this condition.
Input
One four-digit number.
Output
Print "YES" if the number satisfies the specified condition, and "NO" otherwise.
Input example #1
2323
Output example #1
YES
Input example #2
2224
Output example #2
NO