CF626B.Cards

Catherine has a deck of n cards, each of which is either red, green, or blue. As long as there are at least two cards left, she can do one of two actions:

• take any two (not necessarily adjacent) cards with different colors and exchange them for a new card of the third color;
• take any two (not necessarily adjacent) cards with the same color and exchange them for a new card with that color.

She repeats this process until there is only one card left. What are the possible colors for the final card?

凯瑟琳有一副包含 $n$ 张卡片的牌组，每张卡片的颜色为红色、绿色或蓝色中的一种。只要剩余卡片数不少于两张，她就可以执行以下两种操作之一：

• 任取两张（不一定相邻）颜色不同的卡片，并用一张第三种颜色的卡片替换它们；
• 任取两张（不一定相邻）颜色相同的卡片，并用一张同色的卡片替换它们。

她不断重复此过程，直到只剩一张卡片为止。问：最后一张卡片可能是什么颜色？

The first line of the input contains a single integer n (1 ≤ n ≤ 200) — the total number of cards.

The next line contains a string s of length n — the colors of the cards. s contains only the characters 'B', 'G', and 'R', representing blue, green, and red, respectively.

输入的第一行包含一个整数 $n$（$1 \leq n \leq 200$）—— 卡片的总数。

接下来的一行包含一个长度为 $n$ 的字符串 $s$ —— 表示卡片的颜色。$s$ 中仅包含字符 'B'、'G' 和 'R'，分别代表蓝色、绿色和红色。

Print a single string of up to three characters — the possible colors of the final card (using the same symbols as the input) in alphabetical order.

输出一个最多包含三个字符的字符串——最终卡片可能的颜色（使用与输入相同的符号），按字母顺序排列。

In the first sample, Catherine has one red card and one blue card, which she must exchange for a green card.

In the second sample, Catherine has two green cards and one red card. She has two options: she can exchange the two green cards for a green card, then exchange the new green card and the red card for a blue card. Alternatively, she can exchange a green and a red card for a blue card, then exchange the blue card and remaining green card for a red card.

In the third sample, Catherine only has blue cards, so she can only exchange them for more blue cards.

在第一个样例中，凯瑟琳有一张红色卡片和一张蓝色卡片，她必须将它们交换成一张绿色卡片。

在第二个样例中，凯瑟琳有两张绿色卡片和一张红色卡片。她有两种选择：她可以先用两张绿色卡片交换一张绿色卡片，再用这张新得到的绿色卡片和那张红色卡片交换一张蓝色卡片；或者，她可以先用一张绿色卡片和一张红色卡片交换一张蓝色卡片，再用这张蓝色卡片和剩下的绿色卡片交换一张红色卡片。

在第三个样例中，凯瑟琳只有蓝色卡片，因此她只能用蓝色卡片交换更多的蓝色卡片。