import java.io.*;

public class Third {

    static boolean end = false;

    static class Product {
        Character c;

        boolean isUsed() {return c == null;}
        boolean isReady() {return c != null;}
    }

    static class Consumer extends Thread {
        private final Product product;
        PrintWriter pw;

        public Consumer(Product product) {
            this.product = product;
            try {
                pw = new PrintWriter(new FileOutputStream(new File("output.txt")));
            } catch (FileNotFoundException e) {
                throw new IllegalStateException(e);
            }
        }

        @Override
        public void run() {
            while (!end) {
                synchronized (product) {
                    while (!product.isReady()) {
                        try {
                            if(end) break;
                            product.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    useProduct();
                    product.notify();
                }
            }
        }

        void useProduct(){
            if(product.c == null) return;
            pw.print(product.c);
            product.c = null;
            pw.flush();
        }
    }

    static class Producer  extends Thread {

        private final Product product;
        Reader r;

        public Producer(Product product) {
            this.product = product;
            try {
                r = new InputStreamReader(new FileInputStream(new File("input.txt")));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void run() {
            while (!end){
                synchronized (product){
                    while (!product.isUsed()) {
                        try {
                            if(end) break;
                            product.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    buildProduct();
                    product.notify();
                }
            }
        }

        void buildProduct(){
            int in = 0;
            try {
                in = r.read();
            } catch (IOException e) {
                e.printStackTrace();
            }
            if(in == -1) {
                end = true;
                return;
            }
            product.c = (char) in;
        }
    }

    public static void main(String[] args) {
        Product p = new Product();
        Consumer c = new Consumer(p);
        Producer pr = new Producer(p);

        c.start();
        pr.start();
    }

}