S = input()

s = set(list(S))
N = len(S)
C = N * (N + 1) // 2

ans = 0
for c in s:
    ans += 1
    left = 0
    while left < len(S):
        if S[left] == c:
            left += 1
            continue
        right = left
        while right < len(S) and S[right] != c:
            right += 1
        d = right - left
        ans -= d * (d + 1) / (N * (N + 1))
        left = right
print(ans)