/**

*Implement the following operations of a stack using queues.

*push(x) -- Push element x onto stack.

*pop() -- Removes the element on top of the stack.

*top() -- Get the top element.

*empty() -- Return whether the stack is empty.

*/

class Stack {

public:

// Push element x onto stack.

void push(int x) {

q1.push(x);

}

// Removes the element on top of the stack.

void pop() {

while(q1.size()>1)

{

q2.push(q1.front());

q1.pop();

}

q1.pop();

while(!q2.empty())

{

q1.push(q2.front());

q2.pop();

}

}

// Get the top element.

int top() {

while(q1.size()>1)

{

q2.push(q1.front());

q1.pop();

}

int res = q1.front();

q2.push(res);

q1.pop();

while(!q2.empty())

{

q1.push(q2.front());

q2.pop();

}

return res;

}

// Return whether the stack is empty.

bool empty() {

return q1.empty();

}

private:

queue<int> q1,q2;

};