CF141E.Clearing Up

After Santa Claus and his assistant Elf delivered all the presents and made all the wishes come true, they returned to the North Pole and found out that it is all covered with snow. Both of them were quite tired and they decided only to remove the snow from the roads connecting huts. The North Pole has n huts connected with m roads. One can go along the roads in both directions.

The Elf offered to split: Santa Claus will clear up the wide roads and the Elf will tread out the narrow roads. For each road they decided who will clear it: Santa Claus or the Elf. To minimize the efforts they decided to clear the road so as to fulfill both those conditions:

• between any two huts should exist exactly one simple path along the cleared roads;
• Santa Claus and the Elf should clear the same number of roads.

At this point Santa Claus and his assistant Elf wondered which roads should they clear up?

在圣诞老人和他的助手精灵送完所有礼物、实现所有愿望之后，他们回到了北极，发现那里已被积雪覆盖。两人都非常疲惫，于是决定只清理连接小木屋的道路。北极共有 $n$ 个小木屋，由 $m$ 条道路相连，且所有道路均可双向通行。

精灵提议分工合作：圣诞老人负责清理宽路，精灵负责踩实窄路。对于每条道路，他们都已确定由谁来清理：圣诞老人或精灵。为最小化总体劳动量，他们决定按如下两个条件来选择需清理的道路：

• 任意两个小木屋之间，应恰好存在一条仅由已清理道路构成的简单路径；
• 圣诞老人与精灵各自清理的道路数量必须相等。

此时，圣诞老人和他的助手精灵开始思考：究竟应该清理哪些道路？

The first input line contains two positive integers n and m (1 ≤ n ≤ 103, 1 ≤ m ≤ 105) — the number of huts and the number of roads. Then follow m lines, each of them contains a road description: the numbers of huts it connects — x and y (1 ≤ x, y ≤ n) and the person responsible for clearing out this road ("S" — for the Elf or "M" for Santa Claus). It is possible to go on each road in both directions. Note that there can be more than one road between two huts and a road can begin and end in the same hut.

第一行输入包含两个正整数 $n$ 和 $m$（$1 ≤ n ≤ 10^3$，$1 ≤ m ≤ 10^5$）—— 分别表示小屋的数量和道路的数量。接下来是 $m$ 行，每行描述一条道路：该道路所连接的两座小屋的编号 $x$ 和 $y$（$1 ≤ x, y ≤ n$），以及负责清理该道路的人员（“S” 表示精灵，“M” 表示圣诞老人）。每条道路均可双向通行。注意：两座小屋之间可能存在多条道路，且一条道路的起点与终点可以是同一座小屋。

Print "-1" without the quotes if it is impossible to choose the roads that will be cleared by the given rule. Otherwise print in the first line how many roads should be cleared and in the second line print the numbers of those roads (the roads are numbered from 1 in the order of occurrence in the input). It is allowed to print the numbers of the roads in any order. Each number should be printed exactly once. As you print the numbers, separate them with spaces.

如果按照给定规则无法选择需要清理的道路，则输出 "-1"（不带引号）。否则，在第一行输出需要清理的道路数量，在第二行输出这些道路的编号（道路按输入中出现的顺序从 1 开始编号）。允许以任意顺序输出道路编号，每个编号恰好输出一次。输出编号时，用空格分隔。

A path is called simple if all huts on it are pairwise different.

如果一条路径上的所有小屋互不相同，则称该路径为简单路径。