#include <iostream>
#include <vector>
#include <map>

using namespace std;

typedef long long int ll;

int main() {
    //ios::sync_with_stdio(false);

    ll ans = 0;

    char c;
    int prev_i = -1;
    int i = 0;
    int cur_ans = 0;
    while (c = getchar()) {
        if (c == EOF) {
            break;
        }
        bool is_one = c == '1';
        if (is_one) {
            if (prev_i != -1) {
                cur_ans = i - prev_i;
            }
            prev_i = i;
            if (cur_ans > ans) {
                ans = cur_ans;
            }
            cur_ans = 0;
        } else {
            if (prev_i != -1) {
                cur_ans++;
            }
        }
        i++;
    }

    cout << ans / 2 << endl;

}