#include <iostream>
 
template<std::uintmax_t, char...>
struct parse_impl;
 
template<std::uintmax_t Rest>
struct parse_impl<Rest>
{
    static constexpr std::uintmax_t value = Rest / 10;
};
 
template<std::uintmax_t Rest, char Head, char... Tail>
struct parse_impl<Rest, Head, Tail...>
{
    static constexpr std::uintmax_t value = parse_impl<(Rest + (Head - '0')) * 10, Tail...>::value;
};
 
template<char... Number>
struct parse
{
    static constexpr std::uintmax_t value = parse_impl<0, Number...>::value;
};
 
int main() 
{
    std::cout << parse<'1', '2', '3'>::value << '\n';
    std::cout << parse<'4', '7', '9', '2', '5'>::value;
	return 0;
}
 

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