def fib(x):
    seq = [0]
    fib = 0
    while fib < x:
        if len(seq) == 1:
            seq.append(1)
        else:
            fib = seq[-1] + seq[-2]
            seq.append(fib)
    seq.remove(fib)
    return seq
length = raw_input("Up to what number? ")
fiblist = fib(int(length))
i = 0
while i < len(fiblist):
    if fiblist[i] % 2 == 1:
        fiblist.remove(fiblist[i])
    else:
        i = i + 1
print sum(fiblist)