B"There are two strings s and t, consisting only of letters a and b. You can make the following operation several times: choose a prefix of s, a prefix of t and swap them. Prefixes can be empty, also a prefix can coincide with a whole string. Your task is to find a sequence of operations after which one of the strings consists only of a letters and the other consists only of b letters. The number of operations should be minimized. The first line contains a string s (1 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89|s| xe2 x80 x89 xe2 x89 xa4 xe2 x80 x892 xc2 xb7105). The second line contains a string t (1 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89|t| xe2 x80 x89 xe2 x89 xa4 xe2 x80 x892 xc2 xb7105). Here |s| and |t| denote the lengths of s and t, respectively. It is guaranteed that at least one of the strings contains at least one a letter and at least one of the strings contains at least one b letter. The first line should contain a single integer n (0 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89n xe2 x80 x89 xe2 x89 xa4 xe2 x80 x895 xc2 xb7105) -- the number of operations. Each of the next n lines should contain two space-separated integers ai, bi -- the lengths of prefixes of s and t to swap, respectively. If there are multiple possible solutions, you can print any of them. It's guaranteed that a solution with given constraints exists. In the first example, you can solve the problem in two operations: In the second example, the strings are already appropriate, so no operations are needed. "...