#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define all(x) (x).begin(), (x).end()
#define MP make_pair
const int N = 100500;
void solve(){
string s;
cin >> s;
int n = (int)s.size();
int x = n / 2, y = (n + 1) / 2;
long double a = (long double) x * (x - 1) / 4;
long double b = (long double) y * (y - 1) / 4;
cout << fixed << setprecision(6);
cout << a + b << endl;
}
int main() {
ios_base::sync_with_stdio(false);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
solve();
return 0;
}
