typedef std::pair<int, int> Tp;

namespace std
{
    template <>
    struct hash<Tp>
    {
        size_t operator()( const Tp& k ) const
        {
            // Compute individual hash values for first, second and third
            // http://stackoverflow.com/a/1646913/126995
            size_t res = k.first * (1 << 16 + 3) + k.second + 5;
            return res;
        }
    };
}