python valueerror : too many values to unpack

I am a python beginner . I was trying to run this code :

def main():
print ( " This program computes the average of two exam scores . ")
score1,score2 = input ("Enter two scores separated by a comma:")
average = (score1 + score2)/2.0
print ("The average of the score is : " , average )




when I summon the main() I got this ValueError :

ValueError: too many values to unpack (expected 2)




what is wrong with this code ?