test.cpp

#include <iostream>

inline bool isOdd(int num)
{
	return num & 0x01;
}
inline bool numberCheck(int num1, int num2)
{
	if (isOdd(num1) & isOdd(num2))
		return true;
	else if ((!isOdd(num1) & !isOdd(num2)))
		return true;
	else
		return false;
}
int function(int x)
{
	int boundary = 1;
	int seq;

	auto sequence = [] (int n) -> int {
		return (((n - 1) * n) >> 1) + n;
	};

	while (true)
	{
		seq = sequence(boundary);
		if (x <= seq && numberCheck(x, seq))
			break;
		else
			boundary++;
	}

	return boundary;
}
int main(void)
{
	std::cout << function(12) << std::endl;
	return 0;
}