import sequtils, strutils, algorithm

var
    n = readLine(stdin).parseInt
    x = readLine(stdin).split.map(parseInt)
x = x.map(proc(y:int):int = y - min(x))
sort(x, cmp[int])
proc main():string =
    if len(x) != len(deduplicate(x)):
        return "NO"
    var m = x[1] - x[0]
    for i,v in x:
        if i <= 1:
            continue
        if v - x[i - 1] == m:
            continue
        else:
            return "NO"
    return "YES"

echo main()