Conan_Doyle

#include <iostream>
#include <string>
#include <algorithm>
#include <windows.h>

void prepare(std::string& value, char a, char b)
{
  size_t sz = value.size();
  if(sz % 2)
    value.insert(0, 1, b);
  else
    value.insert(sz / 2, 1, a);
}

auto shift = [](const char c, const char a)
{
  return (c != 'Ё') 
         ? (c != 'Е') 
           ? a + ((c - a + 1) % 32)
             : 'Ё' 
               : 'Ж';
};


std::string& process(std::string& s, const char a, const char b, int repeat)
{
  if(!repeat) return s;
  prepare(s, a, b);
  std::transform(s.begin(), s.end(), s.begin(),
    [&](char c){return shift(c, a);
  });
  return process(s, a, b, repeat - 1);
};

int main()
{
  SetConsoleOutputCP(1251);
  std::string one("ВРМ");
  std::string two("ТОР");
  std::cout << process(one, 'А', 'Б', 1) << "\n"  // ВГСН
            << process(two, 'А', 'Б', 2) << std::endl; // ГФБРТ
}