class Solution {
    public int evalRPN(String[] tokens) {
        Stack<String> stack = new Stack<>();
        for(String t: tokens){
            if(!stack.isEmpty() && t.charAt(0)<48 && t.length()==1){
                int num2=Integer.parseInt(stack.pop());
                int num1=Integer.parseInt(stack.pop());
                stack.push(String.valueOf(calculate(num1, num2, t.charAt(0))));
            }else{
                stack.push(t);
            }
        }
        return Integer.parseInt(stack.peek());
    }
    public int calculate(int num1, int num2, char ch){
        switch(ch){
            case '+': return num1+num2;
            case '-': return num1-num2;
            case '*': return num1*num2;
            case '/': return num1/num2;
        }
        return 0;
    }
}