## https://yukicoder.me/problems/no/1329


def main():
    N = input()

    for k in range(1, len(N) + 1):

        low = 2 * (k - 1)
        high = 2 * k

        if low + 1 <= len(N) < high + 1:
            print(k)
            return





    


        

    



if __name__ == "__main__":
    main()