#include <iostream>
#include <string>
#include <type_traits>
#include <utility>
 
using namespace std;
 
template <typename T> T sum(T && x)
{
    return std::forward<T>(x);
}
 
template <typename T, typename ...Args>
typename std::common_type<T, Args...>::type sum(T && x, Args &&... args)
{
    return std::forward<T>(x) + sum(std::forward<Args>(args)...);
}
 
int main()
{
    auto y = sum(1, 2, 4.5); // OK
    cout << y << endl;
 
    auto x = sum(std::string("Hello!"), "World"); // OK
    cout << x << endl;
 
    return 0;
}

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