#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2")
#include "bits/stdc++.h"
using namespace std;
using ll = long long;
int INF = 2e9;
void solve() {
string s;
cin >> s;
ll n = s.size() / 2;
ll ans = (n - 1) * n / 2;
n = s.size() / 2 + s.size() % 2;
ans += (n - 1) * n / 2;
cout << fixed << setprecision(2) << ans / (double)(2);
}
int main() {
ios_base::sync_with_stdio(false);
cout.tie(nullptr);
cin.tie(nullptr);
int queries = 1;
#ifdef test_cases
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
cin >> queries;
#else
// cin >> queries;
#endif
for (int test_case = 1; test_case <= queries; test_case++) {
solve();
// cout << '\n';
}
}
