2003 Honda Element Door lock

2003 Honda Element 4 cyl Four Wheel Drive Automatic

Just bought this car to replace the exact same model a friend totaled. Drove it off the lot and discovered that the key to the driver's door doesn't work. It unlocks the passenger side and the trunk and starts the car. I live in a small town and never lock the door, but sometimes I go to the city, where I do lock up. Is this hard to fix?