import datetime

launch = datetime.date(1977, 9 , 5)
ejup = 1.0921  # Synodic period of Earth-Jupiter
jsat = 19.8584 # Synodic period of Jupiter-Saturn


i = 1 # synodic year earth-jupiter counter
tol = 15 # tolerance in days
while True:
    d1 = datetime.timedelta(days=365.242*ejup*i) # Time of the E-J synodic period
    j = round(ejup*i / jsat) # Nearest J-S synodic period
    d2 = datetime.timedelta(days=365.242*jsat*j) # Time of the J-S synodic period

    # Difference (in days) between the two synodic periods
    dif = abs((d1.total_seconds() - d2.total_seconds()) / 60.0 / 60.0 / 24.0)

    if dif <= tol:
        print("Found matching launch date!")
        print(launch + d1)
        print("Dif:", dif)
        break


    i += 1
    if not i%1000:
        break