# 1/((N+1)*K) == A
# A(1*K+2*K+...+N*K)
# AK(1+2+...+N)
# AK(N(N+1)/2)

N, K = map(int, input().split())
A = 1 / ((N + 1) * K)
print(A * K * (N * (N + 1) / 2))