#include <bits/stdc++.h>
#define int long long
#define lb lower_bound
#define ub upper_bound
#define fi first
#define se second
#define pb emplace_back
#define For(i, x, y) for (int i = (x); i <= (y); i ++)
#define rep(i, x, y) for (int i = (x); i >= (y); i --)
#define pii pair<int, int>
#define all(v) v.begin(), v.end()
#define sz(v) (int)((v).size())
#define ull unsigned long long
#define ls (p << 1)
#define rs (p << 1 | 1)
#define mp make_pair
#define i128 __int128
#define db long double
#define vi vector< int >
#define mem(v, x) memset(v, x, sizeof(v))
#define A3 array< int, 3 >
#define A4 array< int, 4 >
#define vpii vector< pair< int, int > >
using namespace std;
mt19937_64 rnd(time(0));
template< typename T > void cmin(T &x, T y) { return x = min(x, y), void(); }
template< typename T > void cmax(T &x, T y) { return x = max(x, y), void(); }
int ksm(int x, int y, int p) {
    int v = 1; x %= p;
    while (y) v = 1ll * v * ((y & 1) ? x : 1) % p, x = 1ll * x * x % p, y >>= 1;
    return (v % p + p) % p;
}
bool MemoryST;
const int N = 2e5 + 5;
const int mod = 998244353;
const long long INF = 1e18;
const int base = 13131;
void Main() {
	string s; cin >> s;
	int n = sz(s);
	db ans = 0;
	for (int l = 0, r; l < n; l = r + 1) {
		r = l;
		if (s[l] == '0') continue;
		while (r < n && s[r] == '1') r ++;
		r --;
		int x = (r - l + 1);
		if (x % 2) ans += (x + 1) / 2;
		else {
			if (x == 2) ans += sqrt(2);
			else ans += x / 2;
		}
	}
	printf("%.12Lf", ans);
    return;
}
bool MemoryED;
signed main() {
    // ios :: sync_with_stdio(0);
    // cin.tie(0); cout.tie(0);
    cerr << fixed << setprecision(6) << (&MemoryST - &MemoryED) / 1048576.0 << "MB\n";
    int TESTCNT = 1;
    // cin >> TESTCNT;
    while (TESTCNT --) Main();
    cerr << endl << 1e3 * clock() / CLOCKS_PER_SEC << "ms"; 
    return 0;
}