def flatlandSpaceStations(n, c):
    c.sort()
    distances = []
    distances.append(c[0]) # maximum distance of cities before the first station    
    distances.append(n - 1 - c[-1]) # maximum distance of cities beyond the last station
    if len(c) > 1:        
        for i in range(len(c) - 1):
            distances.append((c[i + 1] - c[i]) // 2) # maximum distance of cities between stations
    return max(distances)