app/cses1617.hs

   1 main :: IO ()
   2 main = do
   3   line1 <- getLine
   4   let n = read line1
   5   let solution = solve n 1
   6   print solution
   7
   8 limit = 10 ^ 9 + 7
   9
  10 solve :: Int -> Int -> Int
  11 solve 0 t = t
  12 solve n t = solve (n - 1) ((t * 2) `mod` limit)
  13
  14