1.145 brigades.
Let's say there're an average of 3 brigades per division, that makes nearly 400 divisions for the soviets in 1941.........don't know if that's too far from reality
It's about right if you take the number of units after the mobilization.
Would be less if more units from the border were lost in cauldrons, but we are playing alternative reality here, with Soviets having much better control over their actions.