F,N,K= map(int, input().split())
lis = []
for i in range(1,F+1):
    ans = 0
    for j in range(N):
        if i-j > 0:
           ans += i-j
        else:
           break
    ans = ans *i
    lis.append(ans)
    
        
sum = 0
for i in lis:
    sum += i*1/F**N

print(sum)