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#include <iostream>

int main()
{
	std::ios_base::sync_with_stdio(false); std::cin.tie(0); std::cout.tie(0);
	long k;
	std::cin >> k;
	std::cout << k + 1 << std::endl;
	for (long i = 0; i < k - 1; ++i)
		std::cout << i + 2 << " " << k + 1 << std::endl;
	std::cout << k + 1 << " -1" << std::endl;
	std::cout << "-1 -1" << std::endl;
	return 0;
}