#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
/* DEFINES */
#define F first
#define S second
#define ll long long
#define ull unsigned long long
#define ld long double
#define npos ULLONG_MAX
#define INF LLONG_MAX
#define vv(a) vector<a>
#define pp(a, b) pair<a, b>
#define pq(a) priority_queue<a>
#define qq(a) queue<a>
#define ss(a) set<a>
#define mm(a, b) map<a, b>
#define ump(a, b) unordered_map<a, b>
#define sync \
ios_base::sync_with_stdio(0); \
cin.tie(0); \
cout.tie(0);
#define elif else if
#define endl "\n"
#define allc(a) begin(a), end(a)
#define all(a) a, a + sizeof(a) / sizeof(a[0])
#define pb push_back
#define logi(a) __lg(a)
#define sqrt(a) sqrtl(a)
#define mpr make_pair
#define ins insert
using namespace std;
using namespace __gnu_pbds;
using namespace __cxx11;
typedef char chr;
typedef basic_string<chr> str;
template <typename T, typename key = less<T>>
using ordered_set = tree<T, null_type, key, rb_tree_tag, tree_order_statistics_node_update>;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
void solve()
{
str s;
cin >> s;
ld ln = s.size() - 1;
cout << setprecision(4) << fixed << ln * ln / 8 << endl;
}
/*
*/
int main()
{
sync
// precomp();
ll t = 1;
// cin >> t;
for (ll i = 1; i <= t; i++)
// cout << "Case " << i << ": ",
solve();
cerr << "\nTime elapsed : " << clock() * 1000.0 / CLOCKS_PER_SEC << " ms\n";
}
