#include<bits/stdc++.h> using namespace std; string s; int main() { cin>>s; long long int len = s.length(); if(len %2 == 1) { double fir = len/2; double sec = len/2+1; double ans = (0+fir-1)*fir/4 + (0+sec-1)*sec / 4; printf("%.4lf",ans); } else { double fir = len/2; double sec = len/2; double ans = (0+fir-1)*fir/4 + (0+sec-1)*sec / 4; printf("%.4lf",ans); } return 0; }