#try to avoid input function
a = input("Enter Your branch : 'puc' or 'engg'")
if a == "puc":
b = input("Please enter first 3 characters of your ID :")
if b == "s21" or b == "S21":
print("Your belongs to P1")
elif b == "s20" or b == "S20":
print("Your belongs to P2")
else:
print("Please enter valid input")
elif a == "engg":
b = input("Please enter first 3 characters of your ID :")
if b == "s19" or b == "S19":
print("Your belongs to E1")
elif b == "s18" or b == "S18":
print("Your belongs to E2")
elif b == "s17" or b == "S17":
print("Your belongs to E3")
elif b == "s16" or b == "S16":
print("Your belongs to E4")
else:
print("Please enter valid input")
else:
print("Please enter valid branch")
Click the run button. Try to avoid input() function.