#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
N = [int(x) - ord('0') for x in read().rstrip()]

# %%
dp_0 = 0
dp_1 = 1
for x in N:
    if x == 0:
        dp_0, dp_1 = dp_0, min(1 + dp_1, 1 + dp_0)
    else:
        dp_0, dp_1 = min(1 + dp_0, 1 + dp_1), dp_1

print(dp_0)