def sum_of_multiples(limit):
    sum = 0
    for i in range(1, limit):
        if (i%3 == 0) or (i%5 == 0):
            sum += i
    return sum

def count_DNA(string):
    counts = { 'A': 0, 'C': 0, 'G': 0, 'T': 0 }
    for c in string:
        counts[c] += 1
    return counts