#include <bits/stdc++.h>
using namespace std;
typedef  long long int ll;
#define rep(i, n) for (int i = 0; i < (n); i++)



int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    string s, t = "1000000007";

                   //100000000007
    int ans = 0;
    cin >> s;
    if (s.size() == t.size())
        for (int i = 0; i < t.size(); i++) {
            if (s[i] != t[i] && t[i] == '0')
                ans++;
        }
    if (s.size() > t.size())
        for (int i = 0; i < s.size(); i++) {
            if (s[i] != t[i] && s[i] == '0')
                ans++;
        }

    if (s.size() < t.size())
        for (int i = 0; i < s.size(); i++) {
            if (s[i] != t[i] && t[i] == '0')
                ans++;
        }

    cout << ans << endl;



    return 0;
}