let kamoCount = Int(readLine()!)!

var kamo = readLine()!.split(separator: " ").map{Int($0)!}

kamo.sort{$0<$1}

if(kamo.count != Set(kamo).count) {
    print("NO")
} else {
    let dif = kamo[1]-kamo[0]
    var isValid = true
    for i in 2..<kamoCount {
        if(kamo[i]-kamo[i-1] != dif) {
            isValid = false
            break
        }
    }
    print(isValid ? "YES":"NO")
}