import algorithm, sequtils, strutils

let
  n = parseInt readLine stdin
  xs = stdin
         .readLine
         .split
         .map(parseBiggestInt)
         .sorted
         .deduplicate(true)

if xs.len < n:
  echo "NO"
  quit()

let
  d = xs[1] - xs[0]

for i in 1..<xs.len:
  if xs[i] - xs[i.pred] != d:
    echo "NO"
    quit()

echo "YES"