#include<bits/stdc++.h>
using namespace std;
int n;
string s;
int main(){
    cin>>s;
    n = s.size();
    int ans1 = 0, ans2 = 0;
    for(int i=0;i<n;i++) {
        if(s[i] == '0') continue;
        int j = i;
        while(j < n && s[j] == '1') j++;
        int len = j-i;
        i = j-1;
        if(len & 1) ans1 += (len+1) / 2;
        else ans1 += (len-1) / 2, ans2++;
    }
    double ans = ans1 + ans2 * sqrt(2);
    printf("%.15lf\n", ans);
    return 0;
}