Problem 114

http://projecteuler.net/index.php?section=problems&id=114
普通のDP

import Data.Array.IArray
measure n = mArr!n
    where mArr = listArray (0,n). map m $ [0..n]::Array Int Integer
          m n | n <  3 = 1
              | n == 3 = 2
              | n >  3 = sum [mArr!(n-m-1)| m<-0:[3..n-1]] + 1
main = print.measure$50