def main():
    import sys
    input = sys.stdin.read
    from scipy.linalg import solve
    
    K = int(input().strip())
    
    # 期待値の方程式を構築
    A = [[0] * K for _ in range(K)]
    B = [0] * K
    
    for i in range(K):
        A[i][i] = 1
        for j in range(1, 7):
            if i + j < K:
                A[i][i + j] -= 1 / 6
            else:
                B[i] += 1 / 6
    
    # 連立方程式を解く
    E = solve(A, B)
    
    # 結果を出力
    print(f"{E[0]:.10f}")

if __name__ == "__main__":
    main()