#include <bits/stdc++.h>

using namespace std;

int main() {
  cin.tie(0)->sync_with_stdio(0);
  string s;
  cin >> s;
  double ans = 0;
  for (int l = 0, r; l < s.size(); l++) {
    if (s[l] == '0') continue;
    else {
      r = l;
      while (r < s.size() - 1 && s[r + 1] == '1') r++;
      ans += (r - l + 1) % 2 ? (r - l + 2) * 0.5 : (r - l - 1) * 0.5 + sqrt(2);
      l = r;
    }
  }
  cout << fixed << setprecision(11) << ans << '\n';
  return 0;
}