#include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define REP(i, n) for(ll i = 0;i < n;i++) #define REPR(i, n) for(ll i = n;i >= 0;i--) #define FOR(i, m, n) for(ll i = m;i < n;i++) #define FORR(i, m, n) for(ll i = m;i >= n;i--) #define REPO(i, n) for(ll i = 1;i <= n;i++) #define ll long long #define INF (ll)1 << 60 #define MINF (-1 * INF) #define ALL(n) n.begin(),n.end() #define MOD (ll)1000000007 #define P pair string s; vector cnt[26]; double ans; int main() { cin >> s; REP(i, 26) { cnt[i].push_back(-1); REP(j, s.size()) { if (s[j] - 'a' == i)cnt[i].push_back(j); } cnt[i].push_back(s.size()); double now = 0; REP(j, cnt[i].size() - 1) { ll n = cnt[i][j + 1] - cnt[i][j]; now += n * (n - 1) / 2; } double sz = ((s.size()) *(s.size() + 1) / 2); ans += (sz - now) / sz; } cout << ans << endl; }