What is the guideline here?

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galhajaj

The one and only move here (for a win) is a4

My question is, how can I recognize that, what is the rule/guideline?

My thoughts - 

The kingside is in "deep freeze" and the plan is to bring the king to e6, so I probably need to count moves in the queenside and be the last one to make such move so the opposing king will lose the opposition forcefully.

Am I right with my line of thinking?

There's a short way to count moves or I need to calculate the hard way? There's a method I miss? 

Thanks in advance!

SuryaVS
So you are right, the kingside is frozen. Now, if you freeze the queenside, if your turn to play, draw but if they have to play you win by entering into the territory and taking the pawns. Seeing that, a4-a5 nearly freezes the queenside and gives you extra tempi with the b/c pawns to waste and to infiltrate if you don’t do it immediately black will do a5 and draw. If they do a5 after a4 then c4, b6 b3 and you enter. Hope it clarifies your doubt!
The_King018112

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