That's quite a hard question to answer @Mls1984btc as much would depend on the specifics of the situation.
In all honesty fighting a dog of this size and weight off could be impossible if it is determined to do you harm.
People may suggest various actions to try to stall the dog but these are based on causing the dog fear, pain, or discomfort and are just as likely to inflame the situation further.
Anything you can do to protect your face, neck, chest would be wise. Getting away is obviously also wise- but running can trigger a chase response in the dog.