How to prove this $\sum_{i=1}^{n}(x_{i})^{S-x_{i}}>1?$ Question:

Let $x_{i} \in (0,1),i=1,2,\cdots,n$. Show that
$$
  x_{1}^{S-x_{1}}+x_{2}^{S-x_{2}}+\cdots+x_{n}^{S-x_{n}}>1
$$
where $S=x_{1}+x_{2}+\cdots+x_{n}$.

I have proved when $n=2$,because it use this Bernoulli's inequality
$$
  (1+x)^a\le 1+ax,0<a\le 1,x>-1
$$
so we have
$$
  x^y=\dfrac{1}{(1/x)^y}=\dfrac{1}{\left(1+\frac{1-x}{x}\right)^y}\ge\dfrac{1}{1+\frac{1-x}{x}\cdot y}=\dfrac{x}{x+y-xy}>\dfrac{x}{x+y}
$$
and simaler we have
$$
  y^x>\dfrac{y}{x+y}
$$
so we have
$$
  x^y+y^x>\dfrac{x}{x+y}+\dfrac{y}{x+y}=1
$$

Edit: Now the Mr Michael Rozenberg has prove when $n=3$ and MR Czylabson Asa has prove $n\ge 6$ this inequality can't hold, so how to prove $n=4,5?$
Thanks.


Update
An ugly proof for $n=4$:
Due to symmetry, assume that $d = \max(a, b, c, d)$. Note that
$v\mapsto u^v$ is decreasing on $v > 0$ provided $u\in (0,1)$,
and that $x\mapsto x^y$ is convex on $x>0$ provided $y\ge 1$. We have
\begin{align}
a^{S-a} + b^{S-b} + c^{S-c} + d^{S-d} &\ge a^S + b^S + c^S + d^{S-d}\\
& \ge 3\Big(\frac{a+b+c}{3}\Big)^S + d^{a+b+c}.
\end{align}
Let $a+b+c = 3w$. Then $0 < w \le d < 1$.
It suffices to prove that
$$3w^{3w+d} + d^{3w} \ge 1.$$
It is easy to prove that $w^w > \mathrm{e}^{-1/\mathrm{e}}$ for $w\in (0, 1)$.
Also, we have $d^{3w} \ge \frac{d}{d+ 3w - 3dw}$ by using 
$u^v \ge \frac{u}{u+v-uv}$ for $u>0, \ v\in (0, 1)$.
Thus, it suffices to prove that
$$3\mathrm{e}^{-3/\mathrm{e}}w^d + \frac{d}{d+ 3w - 3dw} \ge 1$$
or
$$3\mathrm{e}^{-3/\mathrm{e}}w^{d-1} \ge \frac{3(1-d)}{d+ 3w - 3dw}.$$
For each fixed $d\in (0, 1)$, let
$$f(w) = \ln \left(3\mathrm{e}^{-3/\mathrm{e}}w^{d-1}\right) - \ln \frac{3(1-d)}{d+ 3w - 3dw}, \quad w\in (0, d].$$
We have
$$f'(w) = \frac{(1-d)d(3w-1)}{w(d+3w-3dw)}.$$
We split into two cases:
1) $d > \frac{1}{3}$: Note that $f'(w) < 0$ on $w\in (0, \frac{1}{3})$ and $f'(w)>0$ on $w\in (\frac{1}{3}, d]$. It suffices to prove that $f(\frac{1}{3}) \ge 0$ or
$$g(d) = \ln \left(3\mathrm{e}^{-3/\mathrm{e}}\right) + (1-d)\ln 3 - \ln (1-d)\ge 0.$$
We have $g'(d) = -\ln 3 + \frac{1}{1-d} \ge -\ln 3 + \frac{1}{1 - 1/3} > 0$. It suffices to prove that $g(\frac{1}{3}) \ge 0$. It is true.
2) $d \le \frac{1}{3}$: Note that $f'(w) \le 0$ on $w\in (0, d]$. It suffices to prove that $f(d) \ge 0$ or
$$\ln \left(3\mathrm{e}^{-3/\mathrm{e}}\right) - (1-d)\ln d - \ln \frac{3(1-d)}{4d - 3d^2}\ge 0$$
or
$$\ln \left(3\mathrm{e}^{-3/\mathrm{e}}\right) + d\ln d - \ln \frac{3(1-d)}{4 - 3d}\ge 0.$$
It is easy to prove that $d\ln d \ge -\frac{1}{\mathrm{e}} + \frac{1}{2}\mathrm{e}\left(d-\frac{1}{\mathrm{e}}\right)^2$
and $ - \ln \frac{3(1-d)}{4 - 3d} \ge -\ln\tfrac{3}{4} + \frac{1}{4}d + \frac{7}{32}d^2$ for $d\in (0, \frac{1}{3}]$.
Thus, it suffices to prove that
$$\ln \left(3\mathrm{e}^{-3/\mathrm{e}}\right)-\frac{1}{\mathrm{e}} + \frac{1}{2}\mathrm{e}\left(d-\frac{1}{\mathrm{e}}\right)^2
-\ln\tfrac{3}{4} + \frac{1}{4}d + \frac{7}{32}d^2 \ge 0.$$
It is true.
We are done.
