Problem:
Score : 300 points

Problem Statement

Given is a sequence of integers A_1, A_2, ..., A_N.
If its elements are pairwise distinct, print YES; otherwise, print NO.

Constraints

2 ≤ N ≤ 200000

1 ≤ A_i ≤ 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 ... A_N

Output

If the elements of the sequence are pairwise distinct, print YES; otherwise, print NO.

Sample Input 1

5
2 6 1 4 5

Sample Output 1

YES

The elements are pairwise distinct.

Sample Input 2

6
4 1 3 1 6 2

Sample Output 2

NO

The second and fourth elements are identical.

Sample Input 3

2
10000000 10000000

Sample Output 3

NO

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define rep(i, a, n) for (int i = (int)(a); i <= (int)(n); ++i)
#define rrep(i, a, n) for (int i = (int)(a); i >= (int)(n); --i)
#define debug(x) cerr << #x << " = " << x << "\n"
#define debugv(x) \
  rep(f, 0, (x.size() - 1)) cerr << x[f] << (f == (x.size() - 1) ? "\n" : " ")
#define debug2(x, y)                       \
  cerr << "(" << #x << "," << #y << ") = " \
       << "(" << x << "," << y << ")\n"
#define all(x) x.begin(), x.end()
#define each(a, x) for (auto& a : (x))
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define int long long
using namespace std;
using pii = pair<int, int>;
using vi = vector<int>;
const int MX = 1e5 + 5, INF = 5LL << 57, MOD = 1e9 + 7;

int N, M;
string S;
vi va, vb;

void input() {
  cin >> N;
  va.resize(N);
  rep(i, 0, N - 1) { cin >> va[i]; };
  ;
}
void solve() {
  set<int> st;
  for (auto x : va) {
    st.insert(x);
  }
  if (st.size() == N) {
    cout << "YES";
  } else {
    cout << "NO";
  }
  cout << endl;

  ;
  ;
}
signed main() {
  input();
  solve();
  return 0;
}