#include <iostream>
#include <ostream>
class A {
  long long counter = 0;

public:
  A() : counter{0} {}
  A operator()() {
    A ret = *this;
    ret.counter++;
    return ret;
  }
  A operator[](int dummy) {
    A ret = *this;
    ret.counter--;
    return ret;
  }
  friend std::ostream &operator<<(std::ostream &lhs, A const &rhs) {
    lhs << rhs.counter;
    return lhs;
  }
};

int main(void) {
  A a;
  std::cout << a[0] << std::endl;
  std::cout << a[0]() << std::endl;
  std::cout << a[0]()() << std::endl;
  return 0;
}