import sequtils,strutils
var
    N = "0" & stdin.readline
    f : bool
    cnt = 0
for i in countdown(N.high, 1):
    if N[i] == '1':
        if f == true and N[i - 1] == '1':
            continue
        elif f == false and N[i - 1] == '1':
            f = true
            cnt += 1
        elif f == true and N[i - 1] == '0':
            N[i - 1] = '1'
            f = false
        elif f == false and N[i - 1] == '0':
            cnt += 1
if N[0] == '1':
    cnt += 1
echo cnt