PairSum Multiple Template Parameters

#include <iostream>
using namespace std;

template<typename A, typename B>
auto pairSum(A a, B b) -> decltype(a+b) {
   return a + b;
}

int main() {
   double a, b;
   cin >> a >> b;
   cout << pairSum(a, b) << "\n";
   return 0;
}