#include <stack>
using namespace std;
int main()
{
    stack<int> st; //presentation of stack
    st.push(5); // push 5 into stack in O(1)
    st.pop(); // pop from stack in O(1)
    st.top(); // top of stack given in O(1)
    st.size(); // size of stack given in O(1)
    st.empty(); // if stack is empty, true otherwise, false given in O(1)
    // in c++11
    stack<int> ts;
    st.swap(ts); // swap two stacks in O(1)
    return 0;
}