dna = input("please enter a dna sequence\n")
A = dna.count("A")
T = dna.count("T")
C = dna.count("G")
G = dna.count("C")
print ( 100*(C+G)/(A+T+C+G) )

print("End1")

#the same as above, but as a function
def GC_content(dna):
     """calculate CG% in string dna"""
     print("CG function")
     A = dna.count("A")
     T = dna.count("T")
     C = dna.count("G")
     G = dna.count("C")
     return 100*(C+G)/(A+T+C+G)

print("End2")