#include <filesystem>
#include <iostream>
#include <string>
#include <algorithm>

int main()
{
    const std::string path = "/proc/";
    for(const auto& entry : std::filesystem::directory_iterator(path))
    {
         if(std::all_of(entry.path().begin(), entry.path().end(), ::isdigit))
             std::cout << entry.path() << '\n';
    }
}