#include <iostream> #include <string> using namespace std; typedef long long llong; int main() { string s; cin >> s; int n = s.size(); llong l = n / 2; llong r = (n + 1) / 2; long double sum = l * (l - 1) / 2LL + r * (r - 1) / 2LL; cout << (double)(sum / 2.000) << endl; return 0; }