// C++ program to sort a stack using an
// auxiliary stack.
#include <iostream>
#include<stack>
#include<queue>
using namespace std;

// This function return the sorted stack
stack<int> swapStack(stack<int> &a,stack<int> &temp)
{


    while(!a.empty())
    {
        int x = a.top();
        a.pop();
        int y = a.top();
        a.pop();

        temp.push(y);
        temp.push(x);


    }
 return temp;

}



int main()
{
    stack<int>a ;

    a.push(1);
    a.push(2);
    a.push(3);
    a.push(4);

    stack<int> temp;
  swapStack(a,temp);


while(!temp.empty())
{
    int ab = temp.top();
    temp.pop();
    cout<<ab<<endl ;
}


}