Project Euler Problem 018

ans1 :: Integer
ans1 = head $ foldr1 f inp where 
  f [] [] = []
  f (x:xs) (a:b:bs) = x+max a b:f xs (b:bs)
--1074  
main :: IO ()
main = print ans1
inp :: [[Integer]]
inp = 
  [ 
    [75],
    [95,64],
    [17,47,82],
    [18,35,87,10],
    [20,4,82,47,65],
    [19,1,23,75,3,34],
    [88,2,77,73,7,63,67],
    [99,65,4,28,6,16,70,92],
    [41,41,26,56,83,40,80,70,33],
    [41,48,72,33,47,32,37,16,94,29],
    [53,71,44,65,25,43,91,52,97,51,14],
    [70,11,33,28,77,73,17,78,39,68,17,57],
    [91,71,52,38,17,14,91,43,58,50,27,29,48],
    [63,66,4,68,89,53,67,30,73,16,69,87,40,31],
    [4,62,98,27,23,9,70,98,73,93,38,53,60,4,23]
  ]