D deme's population was steady at 1245 before it changed to 3399 8770.9 generations ago, maintaining that number to the present.
time_units: generations
demes:
  - name: D
    start_time: .inf
    epochs:
      - start_size: 1245
        end_time: 8770.9
      - start_size: 3399
        end_time: 0