fun main(args: Array<String>) {
    val len = getInt()
    val s = getInts().toSet()
    if (len == s.size) println("YES")
    else println("NO")
}

fun getInt() = readLine()!!.toInt()
fun getInts() = readLine()!!.split(" ").map { it.toInt() }
fun getLong() = readLine()!!.toLong()
fun getLongs() = readLine()!!.split(" ").map { it.toLong() }