import sys
input = lambda : sys.stdin.readline().rstrip()

sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")
debug = lambda x: sys.stderr.write(x+"\n")
writef = lambda x: print("{:.12f}".format(x))


def sub(x):
    if x==1:
        return 1
    v = 0
#     print(f,x)
    p = log(1 - (x-1)/f)
    p1 = log((x-1)/f) if x>1 else 0
#     print(x,p,p1)
    for i in range(k,n+1):
        v += exp(i*p + (n-i)*p1 + cmb(n,i))
    return v
f,n,k = list(map(int, input().split()))
"""数値計算する場合: 対数値を計算する
確率値に戻すときはexpをかませればOK
"""
from math import log, exp
N = n + f + 10 # 必要な最大サイズ
g1 = [0]
v = 0
for i in range(1, N+1):
    v += log(i)
    g1.append(v)
def cmb(n,k):
    return g1[n] - g1[k] - g1[n-k]

ans = 0
for x in range(1,f+1):
    ans += sub(x)
print(ans)