Python homework: Rock Paper Scissors

# 6.189 A Gentle Introduction to Programming

print '***ROCK PAPER SCISSORS***'
pl1 = raw_input("Enter Player 1's choice: ")
value1 = pl1.lower() # convert input into lower case
if value1 == 'rock' or value1 == 'paper' or value1 == 'scissors':
    print 'Player 1: ' + value1
else:
    print 'Invalid input'
pl2 = raw_input("Enter Player 2's choice: ")
value2 = pl2.lower() # convert input into lower case
if value2 == 'rock' or value2 == 'paper' or value2 == 'scissors':
    print 'Player 2: ' + value2
else:
    print 'Invalid input'
if value1 == 'rock' and value2 == 'rock':
    print 'Tie'
elif value1 == 'rock' and value2 == 'scissors':
    print 'Player 1 wins'
elif value1 == 'rock' and value2 == 'paper':
    print 'Player 2 wins'
elif value1 == 'paper' and value2 == 'rock':
    print 'Player 1 wins'
elif value1 == 'paper' and value2 == 'scissors':
    print 'Player 2 wins'
elif value1 == 'paper' and value2 == 'paper':
    print 'Tie'
elif value1 == 'scissors' and value2 == 'rock':
    print 'Player 2 wins'
elif value1 == 'scissors' and value2 == 'scissors':
    print 'Tie'
elif value1 == 'scissors' and value2 == 'paper':
    print 'Player 1 wins'