for(int i=0; i<niza.length; i++) {
            if(niza[i] == "+") {
                int a = stack.pop();
                int b = stack.pop();
                int res = a + b;
                stack.push(res);
            }
            else if(niza[i] == "-") {
                int a = stack.pop();
                int b = stack.pop();
                int res = a - b;
                stack.push(res);
            }
            else if (niza[i] == "*") {
                int a = stack.pop();
                int b = stack.pop();
                int res = a * b;
                stack.push(res);
            }
            else if(niza[i] == "/") {
                int a = stack.pop();
                int b = stack.pop();
                int res = a / b;
                stack.push(res);
            }
            else {
                int p = Integer.parseInt(niza[i]);
                stack.push(p);
            }
        }