import java.util.Arrays;
import java.util.Scanner;

class Main {
    public static void main(String[] args) {
	Scanner sc = new Scanner(System.in);

	int N = sc.nextInt();
	int A[] = new int[N];
	for (int i = 0; i < N; i++)
	    A[i] = sc.nextInt();

	Arrays.sort(A);

	boolean bl = true;
	int check = A[0];
	for (int i = 1; i < N; i++) {
	    if (check == A[i]) {
		bl = false;
		break;
	    }

	    check = A[i];
	}

	if (bl)
	    System.out.println("YES");
	else
	    System.out.println("NO");
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz