Calculating Fibonacci numbers for very large N using Matrices Multiplication Algorithm

Fibonacci.java

import java.math.BigInteger;
import java.util.Scanner;

public class Fibonacci {

    static double num;
    static Runtime runtime = Runtime.getRuntime();
    static long maxMem, allocMem;
    static long startTime, endTime;


    public static void main(String[] args) {

        maxMem = runtime.maxMemory()/(1024*1024);
        allocMem = runtime.totalMemory()/(1024*1024);

        Scanner input = new Scanner(System.in);
        int n = input.nextInt();

        startTime = System.nanoTime();
        System.out.println(effFib(n).mod(BigInteger.TEN));
        endTime = System.nanoTime();

        //System.out.println((endTime - startTime) / 1000000 + " Millisecond");


    }

    private static BigInteger effFib(int n) {

        BigInteger[] matrix = {BigInteger.ONE, BigInteger.ONE, BigInteger.ONE, BigInteger.ZERO};
        return matrixPow(matrix, n)[1];
    }

    private static BigInteger[] matrixPow(BigInteger[] matrix, int n){
        BigInteger[] result = {BigInteger.ONE, BigInteger.ZERO, BigInteger.ZERO, BigInteger.ONE};

        while (n != 0){
            if (n % 2 != 0)
                result = matrixMultiply(result, matrix);

            n /= 2;
            matrix = matrixMultiply(matrix, matrix);
        }

        return result;
    }

    private static BigInteger[] matrixMultiply(BigInteger[] x, BigInteger[] y){
        return new BigInteger[]{
                multiply(x[0], y[0]).add(multiply(x[1], y[2])),
                multiply(x[0], y[1]).add(multiply(x[1], y[3])),
                multiply(x[2], y[0]).add(multiply(x[3], y[2])),
                multiply(x[2], y[1]).add(multiply(x[3], y[3]))
        };
    }

    private static BigInteger multiply(BigInteger x, BigInteger y){
        return x.multiply(y);
    }


}