#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::endl;
using std::string;
int main(){
    string str; cin>>str;
    int N=str.size();
    string S;
    S+='1';
    for(int i=0;i<1e5;i++) S+='0';
    assert((1<=N&&N<=1e5)||str==S);
    assert(str[0]!='0');
    for(int i=0;i<N;i++){
        assert(str[i]>='0'&&str[i]<='9');
    }
    cout<<(N-1)/2+1<<endl;
}