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

signed main() {
	ios::sync_with_stdio(false);
	char x;
	string s;
	cin >> s;
	s += '0';
	int cnt = 0;
	double ans = 0;
	for (size_t i = 0; i < s.size(); i++) {
		if (s[i] == '1') {
			cnt++;
		} else {
			if (cnt == 0) {
				continue;
			}
			if (cnt % 2 == 0) {
				ans += (cnt / 2 - 1);
				ans += sqrt(2);
			} else {
				ans += (cnt / 2 + 1);
			}
			cnt = 0;
		}
	}
	cout << ans << endl;
	return 0;
}