Problem:
Score : 100 points

Problem Statement

It is known that the area of a regular dodecagon inscribed in a circle of radius a is 3a^2.

Given an integer r, find the area of a regular dodecagon inscribed in a circle of radius r.

Constraints

1 \leq r \leq 100

r is an integer.

Input

Input is given from Standard Input in the following format:

r

Output

Print an integer representing the area of the regular dodecagon.

Sample Input 1

4

Sample Output 1

48

The area of the regular dodecagon is 3 \times 4^2 = 48.

Sample Input 2

15

Sample Output 2

675

Sample Input 3

80

Sample Output 3

19200

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

#include <bits/stdc++.h>
#define MAX 100009
#define MOD 1000000007
using namespace std;
typedef long long ll;
typedef vector<long long> vl;

vl v;
set<ll> s;
map<ll, ll> cnt;

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

	v.resize(n);
	for(int i = 0; i < n; ++i)
		cin >> v[i];

	ll ans = 0;
	for(int i = 0; i < n; ++i) {
		auto it = s.lower_bound(v[i]);

		if(s.empty() or it == s.begin()) {
			++ans;
			//cerr << "INS " << v[i] << endl;
			s.insert(v[i]);
		}
		else {
			--it;
			//cerr << "ERR " << *it << " " << v[i] << endl;
			cnt[*it]--;
			if(cnt[*it] == 0)
				s.erase(it);
			s.insert(v[i]);
		}
	}

	cout << ans << endl;
    
    return 0;
}