Special types usage

 #include  <string>
 #include  <iostream>
 int  main()  {
     std::string  s;
     std::cin  >>  s;
     std::string::size_type  a  =  s.find('a');
     std::string::size_type  e  =  s.find('e');
     std::string::difference_type  d  =  e  -  a;
     std::cout  <<  d  <<  '\n';
 }