class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param s string字符串
     * @return int整型
     */
    int calculate(string s) {
        // write code here
        s += '&';
        stack<int> number1;
        stack<char> operation;
        int i = 0;
        int flag = 0;
        int tmp = 0;
        while (i < s.length()) {
            if (s[i] <= '9' && s[i] >= '0') {
                tmp = tmp * 10 + s[i] - '0';
            } else {
                number1.push(tmp);
                tmp = 0;
                if (flag == 1) {
                    int num1 = number1.top();
                    number1.pop();
                    int num2 = number1.top();
                    number1.pop();
                    char opra = operation.top();
                    operation.pop();
                    if (opra == '*')
                        number1.push(num1 * num2);
                    else if (opra == '/')
                        number1.push(num2 / num1);
                    flag = 0;
                }
                if (s[i] == '+' || s[i] == '-' || s[i] == '&') {
                    while (!operation.empty()) {
                        int num1 = number1.top();
                        number1.pop();
                        int num2 = number1.top();
                        number1.pop();
                        char opera = operation.top();
                        operation.pop();
                        if (opera == '+')
                            number1.push(num2 + num1);
                        else if (opera == '-')
                            number1.push(num2 - num1);
                        else if (opera == '*')
                            number1.push(num2 * num1);
                        else if (opera == '/')
                            number1.push(num2 / num1);
                    }
                } else
                    flag = 1;
                operation.push(s[i]);
            }
            i++;

        }
        return number1.top();
    }
};