template <size_t N, typename T>
struct arg_type {

using type = T;
};

template <typename R, typename First, typename... Rest>
struct arg_type<0, std::function<R(First, Rest...)>> {

using type = First;
};


template <size_t N, typename R, typename First, typename... Rest>
struct arg_type<N, std::function<R(First, Rest...)>> {

using type = arg_type<N - 1, std::function<R(Rest...)>>;
};


template<size_t N, typename T>
using arg_type_t = typename arg_type<N, T>::type;

int main() {
   arg_type_t<1, std::function<int (float, double, char)>> value;


std::cout << typeid(value).name();


}