#include <iostream>
#include <set>

int main() {
	int n;
	std::cin >> n;

	std::set<int> set;
	for (int i = 0; i < n; ++i) {
		int a;
		std::cin >> a;

		set.insert(a);
	}

	std::cout << (set.size() == n ? "YES" : "NO") << std::endl;
}