s1 = student("Tom","M")
s2 = student("Jane","F")
s3 = student("John","M")
s4 = student("Ann","F")
s5 = student("Peter","M")
s1.add(80)
s1.add(90)
s1.add(55)
s1.add(77)
s1.add(40)
s2.add(58)
s2.add(87)
s3.add(100)
s3.add(80)
s4.add(40)
s4.add(55)
s5.add(60)
s5.add(60)