Counting brigades and divisions under the command of 1st BF, it would amount roughly to 800.000 soldiers. Based on the Wikipedia entry on Battle of Berlin.
There were 76 divisions and 26 brigades subordinated to the front. I took divisions to have average 10.000 soldiers and a brigade to have 3.000.
Anyway, no less than three quarters of a million to a million men. Roughly.
PS Oh, but there was the 1st Polish army of 5 divisions and a brigade. So subtract some 50 to 60k.