N = [0] + [int(i) for i in input()]
ans = 0
while N:
    if N[-1]==0: N.pop()
    elif len(N)==1: ans += 1; N.pop()
    elif N[-1]==1 and N[-2]==0:
        ans += 1
        N.pop()
    else:
        ans += 1
        while N[-1]==1:
            N.pop()
        N[-1] = 1
print(ans)