#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) printf(__VA_ARGS__)

int dxy[] = {0, 1, 0, -1, 0};

void solve();
signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

/*================================*/

int N,M,Q;
string S;

void solve() {
    cin>>S;
    int ones = 0;
    int ans = 0;
    RREP(i,S.size()) {
        char c = S[i];
        if (c=='0') {
            if (ones == 0) continue;
            if (ones == 1) {
                ans++;
                ones = 0;
                continue;
            }
            char n = S[i-1];
            if (n == '1') {
                ans+=1;
                ones++;
                continue;
            }
            ans += 2;
            ones = 0;
        }
        else {
            ones++;
        }
    }
    if (ones == 1) ans++;
    if (ones > 1) ans += 2;
    
    cout << ans << endl;
}