srecord noeq StupidFib_collab(ICollab collab, int n) {
  // if n <= parallelizationThreshold, we calculate serially
  gettable int parallelizationThreshold = 8;

  selfType parallelizationThreshold(int x) {
    parallelizationThreshold = max(3, x); this;
  }
  
  record noeq Step(int n, LongConsumer continuation) extends LongPairCollector is Runnable {
    void complete(long a, long b) {
      continuation.accept(a+b);
    }
    
    run {
      // fallback to serial case
      if (n < parallelizationThreshold)
        ret with continuation.accept(serialComputation(n));

      collab.addWork(new Step(n-1, setterForA()));
      collab.addWork(new Step(n-2, setterForB()));
    }
  }
  
  long serialComputation(int n) {
    ret stupidFib(n);
  }
  
  long get() {
    // serial or parallel?
    if (collab.coresToUse() == 1)
      ret serialComputation(n);
    else
      ret collab_computeLong(collab, receiver -> new Step(n, receiver));
  }
}