#include <atomic>
#include <cassert>
#include <iostream>
#include <thread>

int main() {
    std::atomic<int> count{0};
    const auto increment = [&] {
        for (int i = 0; i < 1000; ++i) {
            count.fetch_add(1, std::memory_order_relaxed);
        }
    };
    std::thread worker(increment);
    increment();
    worker.join();
    const int total = count.load(std::memory_order_relaxed);
    assert(total == 2000);

    const int old = count.fetch_add(5, std::memory_order_relaxed);
    assert(old == 2000);
    assert(count.load(std::memory_order_relaxed) == 2005);
    std::cout << total << ' ' << old + 5 << '\n';
}