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.
\InputFile
One four-digit number.
\OutputFile
Print "\textbf{YES}" if the number satisfies the specified condition, and "\textbf{NO}" otherwise.
Input example #1
2323
Output example #1
YES
Input example #2
2224
Output example #2
NO