def main():
    start = int(input())
    olymp_coord = int(input())
    portals_qnt = int(input())
    lp_from_start: int = -10**8
    rp_from_start: int = 10**8
    lp_from_olymp: int = -10**8
    rp_from_olymp: int = 10**8
    for _ in range(portals_qnt):
        portal_coord: int = int(input())
        if portal_coord < olymp_coord:
            if portal_coord > lp_from_olymp:
                lp_from_olymp = portal_coord
        elif portal_coord >= olymp_coord:
            if portal_coord < rp_from_olymp:
                rp_from_olymp = portal_coord
        if portal_coord < start:
            if portal_coord > lp_from_start:
                lp_from_start = portal_coord
        elif portal_coord >= start:
            if portal_coord < rp_from_start:
                rp_from_start = portal_coord
    time_to_olymp_from_portal = min([abs(rp_from_olymp - olymp_coord), abs(olymp_coord - lp_from_olymp)])
    time_to_start_from_portal = min([abs(rp_from_start - start), abs(start - lp_from_start)])
    time_through_portal = time_to_olymp_from_portal + time_to_start_from_portal + 1
    time_to_olymp_from_start = abs(start - olymp_coord)
    print(min(time_through_portal, time_to_olymp_from_start))


main()