Love The Lord Your God

In the Gospel of Mark, Jesus said that we should love God with all of our heart, soul, mind, and strength. But in Deuteronomy, it says, "Heart, soul, and strength", in the Gospel of Matthew it says, "Heart, soul, mind", and in the Gospel of Luke it says, "Heart, soul, strength, and mind." Which one is right? And what do they mean? The short answer is that they're all right! And they all say to love the Lord your God with everything you've got.