class Solution {
	stack<int> stk;
	public:
	int evalRPN(vector<string> &tokens)
	{
		vector<string>::iterator it;
		for (it = tokens.begin(); it != tokens.end(); it++)
		{
			string tmp = *it;
			if (isdigit(tmp[0]) || (tmp[0] == '-' && tmp.size() != 1)) stk.push(Convert(tmp));
			else
			{					
				int b = stk.top(); stk.pop();
				int a = stk.top(); stk.pop();
				int c;
				if (tmp[0] == '+') c = a + b;
				else if(tmp[0] == '-') c = a - b;
				else if (tmp[0] == '*') c = a * b;
				else c = a / b;
				stk.push(c);
			}
		}
		return stk.top();
	}
	int Convert(string str);
};
 
int Solution::Convert(string str)
{
	int ans = 0, sig = 1;
	if (str[0] == '-') sig = -1;
	for (int i = 0; i < str.size(); i++)
		if (isdigit(str[i])) ans = ans * 10 + str[i] - '0';
	return ans * sig;
}