N = ['0'] + list(input()) + ['0']
# print (N)
n = len(N)
ans = 0
tmp = n - 2
count = 0
while tmp >= 1:
    if N[tmp] == N[tmp - 1] == '0': #2連続0の時、区切れる
        ans += min(count, 2)
        count = 0
    elif N[tmp - 1] == '0' and N[tmp] == '1' and count == 0:
        ans += 1
    elif N[tmp - 1] == '0' and N[tmp] == '1' and count != 0:
        count += 1
    elif N[tmp - 1] == N[tmp] == '1' and count == 0:
        count = 1
    elif N[tmp - 1] == N[tmp] == '1' and count == 1:
        count = 1
    tmp -= 1

ans += count
print (ans)