For Ilya

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.Scanner;

public class Calc {

    public static void main(String[] args) throws IOException, InterruptedException {
      Scanner scan = new Scanner(System.in);

      System.out.println("Введите пример:");
      String expr = scan.next().replace("+", "%2B");
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://api.mathjs.org/v4/?expr=" + expr))
                .build();

        HttpResponse<String> response = client.send(request,
                HttpResponse.BodyHandlers.ofString());

        System.out.println(response.body());
    }
}