// Greatest Common Denominator (Multi-argument; C++14 version).
 
#include <type_traits>
#include <iostream>
 
template<typename M, typename N>
std::common_type_t<M, N>
gcd(M m, N n)
{
    if (n == 0)
        return m;
    return gcd(n, m % n);
}
 
template<typename M, typename N, typename... Rest>
std::common_type_t<M, N, Rest...>
gcd(M m, N n, Rest... rest)
{
    return gcd(m, gcd(n, rest...));
}
 
// Main.
 
int main()
{
    std::cout << gcd(1, 2) << std::endl;
    std::cout << gcd(2, 4, 6) << std::endl;
    std::cout << gcd(3, 6, 9, 12) << std::endl;
}

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