import sys
def main():
    def input():
        return sys.stdin.readline()[:-1]
    N = input()
    ans = 0
    L = list(N.split("00"))
    if len(L) > 1:
        for l in range(len(L)-1):
            for k in range(len(L[l])):
                e = L[l]
                if e[k] == "1":
                    ans += min(e[k:].count("1"),e[k:].count("0")+2)
                    break
        e = L[-1]
        for k in range(len(e)):
            if e[k] == "1":
                e = e[k:]
                break
        e = e[::-1]
        for k in range(len(e)):
            if e[k] == "1":
                e = e[k:]
                break
        ans += min(e[k:].count("1"),e[k:].count("0")+2)
    else:
        for e in L:
            for k in range(len(e)):
                if e[k] == "1":
                    ans += min(e[k:].count("1"),e[k:].count("0")+2)
                    break
    print(ans)
if __name__ == '__main__':
    main()