import java.util.*

fun main(args: Array<String>) {
    val sc = Scanner(System.`in`)
    val n = sc.nextInt()
    val a: List<Long> = (0 until n).map { sc.nextLong() }
    val distinctA = a.distinct()
    if (a.size > distinctA.size) {
        println("NO")
    } else {
        println("YES")
    }
}