#include <algorithm>
#include <iostream>
#include <string>
#include <thread>
#include <vector>

const size_t THREADS = std::thread::hardware_concurrency();

void CaesarEncryptPart(std::string* s) {
  for (char& c : *s) c = 'a' + (c + 3 - 'a') % 26;
}

void CaesarEncrypt(std::string* s) {
  std::vector<std::thread> threads;
  if (s->length() % 2 != 0) s = s + ' ';
  size_t len = s->length() / THREADS;
  size_t n = std::min(s->length(), THREADS);
  size_t l = 0;
  size_t r = len;
  for (size_t i = 0; i < n; i++) {
    std::string tmp = s->substr(l, r);
    threads.emplace_back(std::thread(CaesarEncryptPart, &tmp));
    l = l + len;
    r = r + len;
  }
  for (size_t i = 0; i < threads.size(); i++) {
    threads[i].join();
  }
}