class MinStack {public:    void push(int x) {        st.push(x);        if (stm.empty() || stm.top() >= x) stm.push(x);    }    void pop() {        int top = st.top(); st.pop();        if (top <= stm.top()) stm.pop();    }    int top() {        return st.top();    }    int getMin() {        return stm.top();    }private:    stack<int> st;    stack<int> stm;};