```
public bool CanWinNim(int n) {
if(n % 4 == 0) return false;
return true;
}
```

if total number of stones are in multiplication of 4, your opponent can use optimal strategy so you can end up with 4 stones and you are doomed.

or else you can use the same strategy to make your opponent end up with stones with multiplication of 4 and make him doomed.