#include <iostream>
#include <set>
using namespace std;
int main() {
    int n, x;
    cin >> n;
    set<int> a;
    for (int i = 0; i < n; i++) {
        cin >> x;
        a.insert(x);
    }
    cout << (a.size() == n ? "YES" : "NO") << endl;
}