Letter Expression

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigDecimal;

public class Demo {
    public static void main(String[] args) throws IOException {
        BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
        String string = r.readLine();

        String number = "";
        Integer countCharacters = 0;
        Integer result = 0;
        BigDecimal currentSum = BigDecimal.valueOf(0);

        for (int i = 0; i < string.length(); i++) {

            char currentChar = string.charAt(i);

            //String builder Append
            if (Character.isDigit(currentChar)) {
                number = number + currentChar;

                if (i == string.length() - 1) {
                    Integer currentNum = Integer.parseInt(number);

                    if (countCharacters % 2 == 0) {
                        result += currentNum;
                    } else {
                        result -= currentNum;
                    }
                    countCharacters = 0;
                    number = "";

                } else if (!Character.isDigit(string.charAt(i + 1))) {
                    Integer currentNum = Integer.parseInt(number);

                    if (countCharacters % 2 == 0) {
                        result += currentNum;
                    } else {
                        result -= currentNum;
                    }

                    countCharacters = 0;
                    number = "";
                }
            } else {
                countCharacters++;
            }

        }

        System.out.println(result);
    }
}