import math
import sys
import decimal

def powerOfTen(n):
    st = str(n)
    if st[0] == '1' and st.count('1') == 1:
        return True
    return False

N = int(input())

logn = math.log10(N)

ans = math.ceil(math.log10(N)/2)

if powerOfTen(N) and logn % 2 == 0:
    ans+=1

print(ans)