给你一个长度为n的，仅由A和B构成的字符串S，每一次操作你可以将一个A变成一个B，也可以将一个B变成一个A。请你求出最少多少次操作后，可以将这个字符串变成一个非递减的字符串？
非递减是指不存在一对 (i,j) ，满足 i<j 且 Si=B,Sj=A 。
给你一个长度为n的，仅由A和B构成的字符串S，每一次操作你可以将一个A变成一个B，也可以将一个B变成一个A。请你求出最少多少次操作后，可以将这个字符串变成一个非递减的字符串？
非递减是指不存在一对 (i,j) ，满足 i<j 且 Si=B,Sj=A 。
样例1
AABBA
样例2
BABBAABABAABBBAABBAAABAABAABBABABBAAABABAABAABBBBAABAAABBBABBBBBBBABBAAAAABBABABBBAABBABAABABBBAABBBBBAAABBBBBBBAABAABBBAAABAAAABBABBBBBAABBABBBBABBBABABBBBAABBAAABBABAABABAAAABABBAAABBAABBABBAAAABBAAAABBBBABAABBAAAAABABABABABBBBAABBAABBAAABBAAABABABBBBAABBAAAABBABABAAABBABBBAABABABBBBAAABBBBBBABAABBAAABBBBABABABBBBBBBBABBBABBBABAAAAAABBBBAABBABBABABBABBAABABAABAAABABBAABABABBBBBBBBBAABBABAABABBABAABAABBABABAABBBBABBAABAAAABABAABBAAAAABBABAAABABBBBBBAABAAABBABABBBAAAABBABABBAAAABAAABBBBBBAAAAABBABAABBBAAABBBBABBABABABBBBAAABBBBBAABABBBBBABAABBABABAAABABABBBAAAAABBAAABABABAABAABBBBABBBABAAABBAAABBABBAABABABBABBBABABBABAABBBBBABBABABBABAABBBBBAAABAABBBBBBBABBBABBBBBBBBBBBAAABABBBAABBBABBBBABAABABABABAABBBAAAABABABBBBBAAABBABBBAABBAABAAAAABAAAAABBABBBAABBBABABAAABABAABAAABBBBBBABABABBBBAABABABBBBABABBABAABBABBBAABBBBBBABAAAAABBBBBAABABABAABABBBBABBBAAABBBBAAABABBBBBBABAAAAABBABAABABAAAAABBAAAAABAABBBABBBAAABBBBBAAAABBBBBBBABBBAABAABBAAABBBBBBBABABBAABABAAAAABABAABAAAAAABBABABABBBBBABBBABAAAAAAABBAABBAAABBBABABAAAAAABBBBAABBABABBBBBAABAABAAAAABABAAAABBAAAABBABBBAABABBABBAAABABABBAABABBBABABBBBBBBABABBABBABAAABBBBABBBAAABABBBBBABAABBABBAABBBABAAABABBABAABABBBAAAABBABBBAAABBABAABABBABABAAABBBBAAAAAABBBABBAABBBBBBAAAABAABAAABBABABAAABAAAABAAABBABABABBABAAABBBAAAAABBBBBAAAAABBBBABABAAABBAAAABBAABAABABABBABBBBAABAAABBABAABABBAABBBAAABABBABABABBAABAAABAABBBBBAABBBABAAAABBBABABBBAABBBAAABABABBABABBABABAABBBABBBBBBBBABBBBABAAABBBABABAABBBBABABBABAAABABBAABABAABBABABABBABABABBBABAAABAABAABBBAABBAABBABBABABAABBBBBABAAABBBBABBBABBBBAABBABABBBBABBBBBBBABBBBABBABBBBABBAABAABAABBAAABAABBBABBBBBABBBAAABAABBAAABAABABBBAABAABABABBBBAAABBBBBABBBBBABAAAAAABAABABABBAABAABAABABBBBBABAABBAAABBBABBBBBBAABABABABBAABBABAAAABBBABAAABBBBAAAAABBABAAABBAABABAABAABBAAABABBAABBBBABAAAABAABBBAABBBABBABAABBBAAABAABBBBBBAABBBBBBBBBABABBBAAAABAAABAAAAABAAAABAAABBBAAABBBBABABBABABABBAABBBBBBBBBBBBAABAABBBBABABBBAABBAABAAAABBBBAABBBBAABBAAABABBABBBBBBBABAAABBBAABBBBAABABAABAAAABBABAAAABBABABABABBABBAABBAAA样例1
1
样例2
926
对于 20% 的数据n≤20 。
对于 40% 的数据n≤100 。
对于 60% 的数据n≤2000 。
对于 100% 的数据，1≤n≤10^6,Si={A,B}