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f = [0] k = 1 ans = 0 for i in range(1, 13): k *= i f.append(k) n, k = map(int, input().split()) soch = list(map(int, input().split())) for i in range(1, len(soch) + 1): ans += (soch[i - 1] - 1) * (f[n - i] // f[n - k]) print(ans)