#include <bits/stdc++.h>
using namespace std;

int main() {
	int N, Ai;
	set<int> A;
	cin >> N;
	for (int i = 0; i<N; i++) {
		cin >> Ai;
		A.insert(Ai);
	}
	cout << (A.size() == N ? "YES" : "NO") << endl;
	return 0;
}
