Actually more than 4m btc lost...today see this https://bitcointalk.org/index.php?topic=2460853.0
Chainalysis's high-end estimate was around 3.8M lost, assuming that Satoshi's 1M are also gone. As they haven't revealed their methodology, their estimate is an argument from authority.
The real figure is more close to around 4.384M lost for good, according to Dr. Myass.