Whats the best possible odds to give?

[ninjia3x]

Heads Up NL holdem.

Each player has 40 dollars to start, blinds are 1-2.

Player A will always get to see Player B's hands b4 preflop betting occurs.

Whats the best possible odds player A can give to B and yet still be marginal +EV?

Math orientiated proof is prefered.

thanks