#include <bits/stdc++.h>
#define int long long
using namespace std;
void solve()
{
  string s;
  cin >> s;
  int cnt = 0;
  double d32 = 0;
  int sq2cnt = 0;
  for (int i = 0; i < s.size(); i++)
  {
    if (s[i] == '1')
    {
      cnt++;
    }
    else
    {
      if (cnt)
      {
        if (cnt & 1)
          d32 += (cnt / 2 + 1);
        else
          d32 += (cnt / 2 - 1), sq2cnt++;
        cnt = 0;
      }
    }
  }
  if (cnt)
  {
    if (cnt & 1)
      d32 += (cnt / 2 + 1);
    else
      d32 += (cnt / 2 - 1), sq2cnt++;
    cnt = 0;
  }
  d32 += sqrtl(2ll * sq2cnt * sq2cnt);
  cout << fixed << setprecision(10) << d32 << endl;
}
signed main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int T = 1;
  // cin>>T;
  while (T--)
  {
    solve();
  }
  return 0;
}