#include <iostream>
using namespace std;

template <typename T,
          typename = enable_if_t<std::is_arithmetic<T>::value, T>>
class Foo {
  T x, y;

public:
  Foo() {
    cout << "x: ";
    cin >> x;
    cout << "y: ";
    cin >> y;
  }

  T sum() { return x + y; };
};

int main() {
  Foo<float> bar;

  cout << bar.sum();

  return 0;
}