Up until 1168.0 generations ago, the count of F deme was 4316. Following that period, it changed to 4257, where it has persisted until now.
time_units: generations
demes:
  - name: F
    start_time: .inf
    epochs:
      - start_size: 4316
        end_time: 1168.0
      - start_size: 4257
        end_time: 0