import std.stdio;

void main() {
	uint[uint] set;
	uint n;

	readf(" %s", &n);

	foreach (i;0..n) {
		uint x;
		readf(" %s", &x);

		if (x in set) {
			writeln("NO");
			return;
		} else {
			set[x] = 1;
		}
	}

	writeln("YES");
}
