import Data.List

fork f (x,y) = (f x, f y)

main = do
 n <- readLn
 as <- map read . words <$> getLine
 print (pyramid n as)

pyramid n as = length ((ipos n as) \\ (ppos (sum as)))

ipos n as = [(x,y) | x <- [1 .. n], y <- [1 .. as!!(x-1)]]

ppos x = do
 let w = floor (sqrt (fromIntegral x))
 iy <- [1 .. w]
 ix <- [iy .. 2*w-iy]
 return (ix,iy)