#include <iostream>

std::size_t A(std::size_t N){

	std::size_t C = 0;

	for (std::size_t i = 0; i < N; i++)
	{
		C += i;
		if (C >= N) return i;
	}

	return C;
}

int main(){
	std::cout << "N=10:" << A(10) << std::endl;
	std::cout << "N=100:" << A(100) << std::endl;
	std::cout << "N=1000:" << A(1000) << std::endl;

	return 0;
}