import std.stdio, std.conv, std.array, std.string, std.algorithm, std.container, std.range, core.stdc.stdlib, std.math, std.typecons;
T[][] combinations(T)(T[] s, in int m) {   if (!m) return [[]];   if (s.empty) return [];   return s[1 .. $].combinations(m - 1).map!(x => s[0] ~ x).array ~ s[1 .. $].combinations(m); }

void main() {
  readln();
  auto A = readln.split.to!(ulong[]).sort();

  void solve() {
    bool[ulong] exists;
    foreach(l; A) {
      if (l in exists) {
        writeln("NO");
        return;
      }
      exists[l] = true;
    }
    writeln("YES");
  }

  solve();
}
