a = []
print 'appending 1'
a.append(1)
print 'appending 2'
a.append(2)
print 'appending 3'
a.append(3)
print 'popping an element'
print a.pop()
print 'appending 4'
a.append(4)
print 'popping an element'
print a.pop()
print 'popping an element'
print a.pop()
