#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; llong sum = l * (l - 1) / 2LL + r * (r - 1) / 2LL; cout << sum / 2; if(sum % 2 == 1) { cout << ".5" << endl; } else { cout << endl; } return 0; }