/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2021.01.08 21:30:25
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    string s;cin >> s;
    if (s[0] == '1') {
        if (s.size()==1) {
            cout << 1 << endl;
        }
        else {
            cout << (s.size()+1)/2 << endl;
        }
    }
    else {
        cout << (s.size()+1)/2 << endl;
    }
    return 0;
}