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

int main() {
    string s;
    std::cin >> s;
    ll n = s.length();
    vector<ll> cnt;
    ll ren0 = 0;
    ll ren1 = 0;
    for (int i = 0; i < n; i++) {
        if(s[i]=='1'){
            if(ren0==0){
                ren1++;    
            }else{
                cnt.push_back(ren0);
                ren0=0;
                ren1=1;
            }
        }else{
            if(ren1==0){
                ren0++;
            }else{
                cnt.push_back(ren1);
                ren1=0;
                ren0=1;
            }
        }
    }
    ll ans = 0;
    cnt.push_back(max(ren0,ren1));
    for (int i = 0; i < cnt.size(); i++) {
        if(i%2==0){
            if(cnt[i]==1){
               ans++; 
            }else{
                // 押し付けられるとき
                if(i<cnt.size()-2 && cnt[i+1]==1 && cnt[i+2]!=1){
                    ans++;
                }else{
                    ans+=2;
                }
            }
        }
    }
    std::cout << ans << std::endl;
}