import java.util.*;

class Main {

	static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		Map<Integer, Boolean> A = new TreeMap<Integer, Boolean>();
		boolean ans = true;
      	int N = sc.nextInt();
		for (int i = 0; i < N; i++) {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		}
		System.out.println(ans ? "YES" : "NO");
	}
} import java.util.*; util.* java class Main {

	static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		Map<Integer, Boolean> A = new TreeMap<Integer, Boolean>();
		boolean ans = true;
      	int N = sc.nextInt();
		for (int i = 0; i < N; i++) {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		}
		System.out.println(ans ? "YES" : "NO");
	}
} Main static Scanner sc = new Scanner(System.in); sc new Scanner(System.in) public static void main(String[] args) {
		Map<Integer, Boolean> A = new TreeMap<Integer, Boolean>();
		boolean ans = true;
      	int N = sc.nextInt();
		for (int i = 0; i < N; i++) {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		}
		System.out.println(ans ? "YES" : "NO");
	} main {
		Map<Integer, Boolean> A = new TreeMap<Integer, Boolean>();
		boolean ans = true;
      	int N = sc.nextInt();
		for (int i = 0; i < N; i++) {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		}
		System.out.println(ans ? "YES" : "NO");
	} Map<Integer, Boolean> A = new TreeMap<Integer, Boolean>(); A new TreeMap<Integer, Boolean>() boolean ans = true; ans true int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc for (int i = 0; i < N; i++) {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		} {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		} int temp = sc.nextInt(); temp sc.nextInt() sc.nextInt sc if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			} !A.containsKey(temp) A.containsKey(temp) A.containsKey A temp {
				A.put(temp, true);
			} A.put(temp, true) A.put A temp true {
				ans = false;
				break;
			} ans = false ans false break; System.out.println(ans ? "YES" : "NO") System.out.println System.out System System.out ans ? "YES" : "NO" ans "YES" "NO" String[] args args
import java.util.*;

class Main {

	static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		Map<Integer, Boolean> A = new TreeMap<Integer, Boolean>();
		boolean ans = true;
      	int N = sc.nextInt();
		for (int i = 0; i < N; i++) {
			int temp = sc.nextInt();
			if (!A.containsKey(temp)) {
				A.put(temp, true);
			} else {
				ans = false;
				break;
			}
		}
		System.out.println(ans ? "YES" : "NO");
	}
}