public int evalRPN(String[] tokens) {
    		int len=tokens.length;
    		Stack<Integer> stack=new Stack<Integer>();
    		for(int i=0;i<len;i++){
    			if(!tokens[i].equals("+")&&!tokens[i].equals("-")&&!tokens[i].equals("*")&&!tokens[i].equals("/")){
    				stack.push(Integer.valueOf(tokens[i]));
    			}else{
    				int op2=stack.pop();
    				int op1=stack.pop();
    				if(tokens[i].equals("+")){
    					stack.push(op1+op2);
        			}else if(tokens[i].equals("-")){
        				stack.push(op1-op2);
        			}else if(tokens[i].equals("*")){
        				stack.push(op1*op2);
        			}else if(tokens[i].equals("/")){
        				stack.push(op1/op2);
        			}
    			}
    		}
        return stack.pop();
    }