package fibonacci;

public class FibonacciTask {

	public static void main(String[] args) {

		System.out.println(calculateEvenFibonacciNumbersBefore4000000Sum());

	}
	// Finds the sum of the even-valued Fibonacci sequence terms, whose values do not exceed four million
	// I didn't use recursive fibonacci numbers algorithm, because i think this one is more optimal
	static int calculateEvenFibonacciNumbersBefore4000000Sum(){

		int prev = 0, next = 1, fibonacciNumber = 0, sum = 0;

		while (fibonacciNumber <= 4000000){

				if(isEven(fibonacciNumber))

					sum += fibonacciNumber;

				fibonacciNumber = prev + next;

				prev = next;

				next = fibonacciNumber;

			}
		return sum;
	}

	// Parity check
	static boolean isEven(int number){

		return number % 2 == 0;

	}

}