#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<tuple>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define Per(i,sta,n) for(int i=n-1;i>=sta;i--)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;

string s;
int n;

void solve(){
    cin >> s;
    n=s.length();
    vector<char> t;
    per(i,n){
        t.push_back(s[i]);
    }
    t.push_back('0');
    rep(i,n+1){
        //cout << t[i] << endl;
    }
    int ans=0;
    rep(i,t.size()){
        if (t[i]=='1'){
            if(i!=t.size()-1){
            if (t[i+1]=='0'){
                if (i>0) {
                    if(t[i-1]=='0'){
                        ans+=1;
                        t[i]='0';
                    }
                    else{
                        t[i+1]='1';
                        t[i]='0';
                        ans+=1;
                    }
                }
                else{
                    t[i]='0';
                    ans+=1;
                }
            }
            }
            else{
                ans+=1;
            }
        }
    }

    cout << ans << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(50);
    solve();
}