In the below Question the print statement is only supposed to give as VALID or INVALID but sometimes it gives string other than that. Can someone expl [closed]

import re 
a=input()
if re.match("[0-3][0-9]-[0-1][0-9]-[0-2][0-9][0-9][0-9]",a):
    b=int(a[6:10])
    if b%4==0:
        c=int(a[3:5])
        if c==1 or c==3 or c==5 or c==7 or c==8 or c==10 or c==12:
            d=int(a[0:2])
            if d<32:
                print("VALID")
            else:
                print("IN VALID")
        elif c==4 or c==6 or c==9 or c==11 :
            d=int(a[0:2])
            if d<31:
                print("VALID")
            else:
                print("IN VALID")
        elif c==2:
            d=int(a[0:2])
            if d<30:
                print("VALID")
            else:
                print("IN VALID")
        else:
            print("IN VALID")
    else:
        c=int(a[3:5])
        if c==1 or c==3 or c==5 or c==7 or c==8 or c==10 or c==12:
            d=int(a[0:2])
            if d<32:
                print("VALID")
            else:
                print("IN VALID")
        elif c==4 or c==6 or c==9 or c==11 :
            d=int(a[0:2])
            if d<31:
                print("VALID")
            else:
                print("IN VALID")
        elif c==2:
            d=int(a[0:2])
            if d<29:
                print("VALID")
            else:
                print("IN VALID")
        else:
            print("IN VALID")
else:
    print("IN VALID")

##had written this coded in python to verify if a date given as a input is valid or not including leap year. Because I just started learning python this was the only way i could think to solve it. it works fine for most dates but when i input some particular values i get this as my answer Output with varying degree of correctness

I don't know how it is being printed as in print statement only ("VALID") or ("Invalid") is given.Can someone please explain where it goes wrong.