CF343B Alternating Current
题目描述
两条电线分别插入了正确的位置，但是缠绕在一起，如下图所示。
电线不能被剪断或断开，插入的设备也不能被移动，请问是否可以在这种情况下解开电线？
为了更好地理解题意，请阅读样例的解释。
输入格式
输入一行包含字符为 `+` 和 `-` 的字符序列$(1 \le n \le 1000000)$。
第 $i$ 个位置上如果是 `+`，说明此位置正极在负极上方；如果是 `-`，说明此位置负极在正极上方。
输出格式
输出一行，若能解开则输出 `Yes`，否则则输出 `No`。
说明/提示
The first testcase corresponds to the picture in the statement. To untangle the wires, one can first move the "plus" wire lower, thus eliminating the two crosses in the middle, and then draw it under the "minus" wire, eliminating also the remaining two crosses.
In the second testcase the "plus" wire makes one full revolution around the "minus" wire. Thus the wires cannot be untangled:
In the third testcase the "plus" wire simply runs above the "minus" wire twice in sequence. The wires can be untangled by lifting "plus" and moving it higher:
In the fourth testcase the "minus" wire runs above the "plus" wire once. The wires cannot be untangled without moving the device itself:
