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 "iomanip"
#include "algorithm"
#include "iostream"
#include "string"
#include "vector"
#define rep(i, to) for (ll i = 0; i < (to); ++i)
#define rep1(i, to) for (ll i = 1; i <= (to); ++i)
#define all(vec) vec.begin(), vec.end()
#define unless(cond) if (!(cond))
using namespace std;
typedef long long ll;
template <typename T>
using V = vector<T>;

template <typename T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}

template <typename T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

template <typename T>
void drop(const T& x) {
  cout << x << endl;
  exit(0);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N;
  cin >> N;
  V<ll> as(N);
  for (auto& a : as) cin >> a;

  sort(all(as));

  rep(i, N - 1) {
    if (as[i] == as[i + 1]) {
      drop("NO");
    }
  }

  cout << "YES" << endl;
}