import java.util.Arrays;

class CustomString {

    private static String concatenate(String... inputs) {

        var stringSize = Arrays.stream(inputs).mapToInt(input -> input.toCharArray().length).sum();
        var newInputCharArray = new char[stringSize];

        int index = 0;

        for (String input : inputs) {
            var inputCharArray = input.toCharArray();

            for (int x = 0; x < inputCharArray.length; ++x, ++index) {
                newInputCharArray[index] = inputCharArray[x];
            }
        }
        return new String(newInputCharArray);
    }

    public static void main(String[] args) {
        System.out.println(concatenate("Hel", "lo", " ", "Wor", "ld."));
    }
}