#include <bits/stdc++.h>
#define ll long long int
using namespace std;


int main(){
ll k;
cin>>k;

set<ll>s;
for(ll i=0;i<k;i++)
{
    ll l;
    cin>>l;
    s.insert(l);
}
ll k1=s.size();
if(k!=k1)
{
    cout<<"NO";
}
else
{
    cout<<"YES";
}
    
}
