#include <iostream>
#include <iomanip>
#include <chrono>
#include <ctime>
int main() {
auto now = std::chrono::system_clock::now();
std::time_t now_t = std::chrono::system_clock::to_time_t(now);
std::tm* now_tm = std::gmtime(&now_t);
std::cout << std::put_time(now_tm, "%Y-%m-%d %H:%M:%S") << "."
<< std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count() % 1000
<< std::endl;
}
/*
run:
2024-09-20 06:59:37.860
*/