#define _CRT_SECURE_NO_WARNINGS
#include <stdbool.h>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <ctype.h>

void main()
{
	int n, a[150];
	bool x = false;
	scanf("%d", &n);
	for (int i = 0; i < n; i++)
	{
		scanf("%d", &a[i]);
	}
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < n; j++)
		{
			if (a[i] == a[j] && j != i)
				x = true;
		}
	}
	x ? printf("NO") : printf("YES");
}