rr = raw_input
rri = lambda: int(raw_input())
rrm = lambda: map(int, raw_input().split())

def solve(A):
    dp0 = 0
    dp1 = 1 << 30
    for x in A:
        if x:
            dp0,dp1 = min(dp0+1, dp1+2), min(dp0, dp1)
        else:
            dp0,dp1 = min(dp0, dp1+2), min(dp0,dp1)+1
    return min(dp0, dp1 + 2)

print solve(map(int, rr()))