The program below is handling a stack container. What is the output of running the program?

#include <iostream>
#include <stack>
int main()
{
    std::stack<int> stack;
    stack.push(1);
    stack.push(2);
    stack.push(3);
    stack.pop();
    stack.push(4);
    stack.top();
    stack.pop();
    std::cout << stack.top();
}