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

#define REP(i, m, n) for (int i = (m); i < (int)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define reps(i, n) for (int i = 0; i <= (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
typedef long long ll;
typedef pair<int, int> P;
const int inf = INT_MAX;
const ll INF = 1LL << 60;
const ll mod = 1e9 + 7;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    string s; cin >> s;
    ll n = s.size();
    ll cnt = 0;
    vector<int> a;
    vector<int> zero(n);
    rep(i, n-3) {
        if (s[i] == '1' && s[i+1] == '0' && s[i+2] == '1' && s[i+3] == '1') {
            zero[i+1] = 1;
        }
        else if (s[i] == '1' && s[i+1] == '1' && s[i+2] == '0' && s[i+3] == '1') {
            zero[i+2] = 1;
        }
    }
    ll ans = 0;
    rep(i, n) {
        if (s[i] == '1') {
            cnt++;
        } else if (cnt && zero[i]) {
            ans++;
        } else if (cnt) {
            a.pb(cnt);
            cnt = 0;
        }
    }
    if (cnt) a.pb(cnt);
    // rep(i, a.size()) cout << a[i] << ' ';
    // cout << endl;
    rep(i, a.size()) {
        if (a[i] >= 2) {
            ans += 2;
        } else {
            ans++;
        }
    }
    cout << ans << endl;
    return 0;
}