A string of letters $A, B$, $C$ is forbidden if there are three consecutive letters from which one is $A$, one is $B$ and one is $C$. For example, $BAACAACCBAAA$ is forbidden, while $AABBCCAABB$ is not. How many such strings of length $n$ are not forbidden? \InputFile Each line contains one number $n~(1 \le n \le 30)$. \OutputFile For each input value of $n$ print in a separate line the number of strings of length $n$ are not forbidden.