-java: algo

Fib.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicReference;

import static com.jayway.awaitility.Awaitility.await;
import static java.lang.Integer.parseInt;
import static java.lang.System.in;
import static java.math.BigInteger.ONE;
import static java.math.BigInteger.ZERO;
import static java.util.concurrent.TimeUnit.MILLISECONDS;

/**
 * @author Alexander Krasniansky
 */
public class Fib {

    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));

        final int n = parseInt(reader.readLine());
        final AtomicReference<BigInteger> res = new AtomicReference<>();

        await().atMost(100, MILLISECONDS).until(new Callable<Boolean>() {
            public Boolean call() throws Exception {
                res.set(fib(n));
                return true;
            }
        });

        String resultAsString = res.get().toString();
        int length = resultAsString.length();

        System.out.println(resultAsString.charAt(length - 1));

        reader.close();
    }

    private static BigInteger fib(int n) {
        BigInteger[] ints = new BigInteger[n + 1];

        ints[0] = ZERO;
        ints[1] = ONE;

        for (int i = 2; i <= n; i++) {
            ints[i] = ints[i - 1].add(ints[i - 2]);
            ints[i - 2] = null;
        }

        return ints[ints.length - 1];
    }
}

Solution for: https://stepic.org/lesson/%D0%A7%D0%B8%D1%81%D0%BB%D0%B0-%D0%A4%D0%B8%D0%B1%D0%BE%D0%BD%D0%B0%D1%87%D1%87%D0%B8-13228/step/7?course=%D0%90%D0%BB%D0%B3%D0%BE%D1%80%D0%B8%D1%82%D0%BC%D1%8B-%D1%82%D0%B5%D0%BE%D1%80%D0%B8%D1%8F-%D0%B8-%D0%BF%D1%80%D0%B0%D0%BA%D1%82%D0%B8%D0%BA%D0%B0-%D0%9C%D0%B5%D1%82%D0%BE%D0%B4%D1%8B&unit=3414

It does not work (Time Limit).