#include <iostream>

template <typename T1, typename T2>
auto sum(T1 a, T2 b) -> decltype(a+b) { return a + b; }

int main()
{
  auto x = 3;
  decltype(x) y = x; 

  std::cout << x << ' ' << y << ' ' << sum(x,y) << '\n';
}