#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,i,x;
				set<int> s;
    cin>>n;
    for(i=0;i<n;i++){
        cin>>x;
        s.insert(x);
    }
    if(s.size()==n) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
}