Аритметички израз

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ArithmeticExpression {

    static int operate(int op, int op2, char op3) {
        if (op3 =='+')
            return op + op2;
        else
            return op - op2;
    }

    static int presmetaj(char c[], int l, int r) {

        if (r - l ==4)
            return operate(c[l+1]-'0',c[l+3]-'0',c[l+2]);

        int flag =0;
        int i=l;

        while ((c[i] != '+'&&c[i] != '-') || flag !=1){

            if (c[i] == '(')
                flag++;
            else if (c[i] == ')')
                flag--;

            ++i;
        }
            return operate(presmetaj(c,l+1,i-1),presmetaj(c,i+1,r-1),c[i]);
    }

    public static void main(String[] args) throws Exception {
        int i,j,k;

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String expression = br.readLine();
        char exp[] = expression.toCharArray();

        int rez = presmetaj(exp, 0, exp.length-1);
        System.out.println(rez);

        br.close();

    }

}