text: #include <vector>
  #include <iostream>
  using namespace std;
  
  string a(string s)
  {
    s[0] += 2;
    s.push_back(s[0]);
    return s;
  }
  
  main(int argc, char **argv)
  {
    vector <string> v;
    int i;
  
    v.push_back("A");
    for (i = 0; i < 4; i++) v.push_back(a(v[i]));
    for (i = 0; i < v.size(); i++) cout << v[i] << endl;
  }
  