#include<bits/stdc++.h>
#include<bits/extc++.h>
#define stl_priority_queue std::priority_queue
#define pbds_priority_queue __gnu_pbds::priority_queue
#define endl '\n'
#define Endl cout<<endl
#define Made return
#define by 0
#define Barry +0
#define fre(x) freopen(x".in","r",stdin);freopen(x".out","w",stdout);
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
string s;
int main(){
    //fre("name");
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    cin>>s;
    cout<<s.size()-count(s.begin(),s.end(),'0')+(count(s.begin(),s.end(),'0')+1)/2<<endl;
    Made by Barry;
}

样例全过WA一半