def complement(dna):
    complement_dna = {"A":"T","C":"G","T":"A","G":"C"}
    dna = dna.upper()
    n = list(dna)
    strand = ""
    for l in n:
        if l in complement_dna:
            strand = strand + complement_dna[l]
        else:
            print("Must contain only A, C, T, or G")
    return strand


def reverse_complement(dna):
    rev = complement(dna)
    reverse = ""
    length = len(dna) - 1
    while(length >= 0):
        reverse = reverse + rev[length]
        length = length - 1
    return reverse

dna = str(input("Input DNA strand: "))
print ("Complement: ", complement(dna))
print ("Reverse Complement: ", reverse_complement(dna))