#include <iostream>
 #include <type_traits>
 #include <typeinfo>

 template<typename T1, typename T2, typename R = typename std::conditional <(sizeof(T1) < sizeof(T2)), T1, T2>::type >
 R gcd(T1 a, T2 b){
   static_assert(std::is_integral<T1>::value, "T1 should be an integral type!");
   static_assert(std::is_integral<T2>::value, "T2 should be an integral type!");
   if( b == 0 ){ return a; }
   else{
     return gcd(b, a % b);
   }
 }

 int main(){

   std::cout << std::endl;

   std::cout << "gcd(100,10)= " <<  gcd(100,10)  << std::endl;
   std::cout << "gcd(100,33)= " << gcd(100,33) << std::endl;
   std::cout << "gcd(100,0)= " << gcd(100,0)  << std::endl;

   std::cout << std::endl;

   std::cout << "gcd(100,10LL)= " << gcd(100,10LL) << std::endl;

   std::conditional <(sizeof(100) < sizeof(10LL)), long, long long>::type uglyRes= gcd(100,10LL);
   auto res= gcd(100,10LL);
   auto res2= gcd(100LL,10L);

   std::cout << "typeid(gcd(100,10LL)).name(): " << typeid(res).name() << std::endl;
   std::cout << "typeid(gcd(100LL,10L)).name(): " << typeid(res2).name() << std::endl;

   std::cout << std::endl;

 }