#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define ff first
#define ss second
#define all(s) s.begin(),s.end()
#define rall(s) s.rbegin(),s.rend()
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
using ld=long double;
string s;
cin>>s;
sort(all(s));
assert(s[0]==s.back());
ll n=s.size();
ll L=n/2,R=(n+1)/2;
cout<<setprecision(3)<<(L*(L-1)/2+R*(R-1)/2)/2.0;
}
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