Submission #1525576

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Source Code Expand

#include <bits/stdc++.h>
#define rep(i, a, b) for(int i=a; i<b; i++)

using namespace std;

typedef long long ll;

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

  map<ll, int> m;
  
  int n;
  cin >> n;
  rep(i, 0, n){
    ll a;
    cin >> a;
    m[a]++;
  }

  ll sq = -1;
  vector<ll> v;
  for(auto p: m){
    if( p.second >= 2 )
      v.push_back(p.first);
    if( p.second >= 4 )
      sq = max(sq, p.first);
  }

  if( v.size() < 2 ){ // No rectangle possible
    if( sq != -1 ) // But square possible
      cout << sq*sq << endl;
    else
      cout << 0 << endl;
  }else{
    n = v.size();
    ll reca = v[n-1]*v[n-2];

    if( reca > sq*sq )
      cout << reca << endl;
    else
      cout << sq*sq << endl;
  }
  

  return 0;
}

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