#include <string>
#include <iostream> // for the demo only
std::string concat(std::string const& a) {
return a;
}
template <typename... Items>
std::string concat(std::string const& a, std::string const& b, Items&&... args) {
return concat(a + b, args...);
}
int main() {
std::cout << concat("0", "1", "2", "3") << "\n";
}
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