def flatlandSpaceStations(n, c):
    c.sort()
    distances = []
    
    # first
    distances.append(c[0])

    # pair
    for i, city_with_space_station_idx in enumerate(c):
        if i==len(c)-1:
            break
        next_city_idx = c[i+1]
        diff = next_city_idx  - city_with_space_station_idx - 1       
        distances.append(math.ceil(diff/2))
    # last
    distances.append(n-c[-1]-1)
    
    return max(distances)