F, N, K = map(int, input().split())

"""
dp[i,j,k,l]: i回投げた、jが合計k回でた、jより大きい値がl回出た
"""
dp = [[[0]*(N+1) for _ in range(N+1)] for _ in range(F)]
for i in range(F):
    dp[i][0][0] = 1

for cnt in range(1, N+1):
    newDP = [[[0]*(N+1) for _ in range(N+1)] for _ in range(F)]
    for i in range(F):
        for j in range(cnt):
            for k in range(cnt):
                if j + k > cnt:
                    break
                newDP[i][j+1][k] += dp[i][j][k]/F
                newDP[i][j][k+1] += (F-(i+1))*dp[i][j][k]/F
                newDP[i][j][k] += i*dp[i][j][k]/F
    dp = newDP

ans = 0
for i in range(F):
    for j in range(N+1):
        for k in range(N+1):
            if j + k > N:
                continue
            if k >= K:
                continue
            if j + k >= K:
                ans += dp[i][j][k] * (i + 1)


print(ans)