Only one.

WHY? His only "mobile" N, being the other unable to act!!! Was g4 a better option?

threatening 47.a4 followed by b5.. giving the B extra duty.

I tried Nc3 for white, thinking in creating an obstruction in e5 so the K can take the c pawn... but it doesn't work! 46. Nc3, Ke5!, and e4 doesn't work because of Bxe4, NxB, KxN, and white's position is lost since black's h and g pawns promote faster than white's... true? More interesting is 46. Nd4, threatening NxB and Kxc2 a tempo BEFORE, but still unable to promote before black. White's play was more than accurate in this aspect! I would have fell for it. But white can have other ideas in mind, like Nc6, b4, Nb8, winning the a pawn and threatening promotion on his own...

White's desperate: he will lose the N, that's all. But maybe, with some help from black...

Interesting variation by Justin, but I wonder why black has to move the bishop on move 54 at all in that variation - isn't it already perfectly place on f5 where it can watch the pawn on c7 and control h3. I wonder if white has any improvement rather than just moving his pieces back and forth, for instance Kd7 52. Nf3 Kc7 53. Ng5 Kb6 54. e4. Also why does black have to approach the g pawn via d7 rather than d6 and c5?

Further computer analysis reveals that 54...Bg6! is the winning move (instead of Be4). The difference is that Nh3-Nf2 making possible e4 to block the LSB is played with tempo in case of Be4 (Nf2 hits the bishop on e4), whereas with it already on Bg6, the black king has time to get to b3 and protect the pawn right after white plays e4, never allowing the c-pawn to be captured. The knight will have to give itself for the h-pawn eventually, and then black's c-pawn proves decisive. Fascinating the difference one tempo can make! Edit: (Reply to Charles) - First of all, If the Black king tries to approach via d6, instead of d7, it's too close to the action, and can get forked by the a knight on e4 or f5. Consider 51... Kd6 52. Nf3 h3 53. e4! Bxe4 54. Ng5 h2 55. Nxe4+ (the key difference is this is with check). Now the knight has time to get to f2 and stop the pawn. Also in that line if Black avoids 53...Bxe4 and plays instead 53...Bg6, then 54. e5+ and the pawn keeps marching, and eventually black gives up the bishop for the pawn, and white's knight stops the h-pawn. I'll reply more in another comment on the next move for aesthetic reasons.

Another reply to Charles: If the bishop stays on f5 in the key variation (instead of 54...Bg6, black plays 54...Kxb5?) then 55. Nf3 h3 (to save the pawn), and there's another fork 56. Nd4+ Kc4 57. Ng3 and the pawn is stopped again. Finally if white tries to not simply shuffle his king back and forth, we have 51...Kd7 52. Nf3? h3! (not Kc7), and now white is still forced to just shuffle back and forth, as the knight can't leave watch of h2. Eventually the black king can take the b-pawn (as long as the black bishop is not on f5 because of Nd4+), and then the e-pawn and escort the h-pawn home against the knight, with the bishop protecting the pawn on c2. The white king has to stand permanent guard there.