Codeforces Round #442 (Div. 2) B

题目链接：http://codeforces.com/contest/877/problem/B

B. Nikita and string

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

One day Nikita found the string containing letters "a" and "b" only.

Nikita thinks that string is beautiful if it can be cut into 3 strings (possibly empty) without changing the order of the letters, where the 1-st and the 3-rd one contain only letters "a" and the 2-nd contains only letters "b".

Nikita wants to make the string beautiful by removing some (possibly none) of its characters, but without changing their order. What is the maximum length of the string he can get?

Input

The first line contains a non-empty string of length not greater than 5 000 containing only lowercase English letters "a" and "b".

Output

Print a single integer — the maximum possible size of beautiful string Nikita can get.

Examples

input      abba

output    4

input       bab

output     2

Note

It the first sample the string is already beautiful.

In the second sample he needs to delete one of "b" to make it beautiful.

题意：给定一个只含ab的字符串，要将字符串分为3段前一段和后一段只包含a,中间只包含b，可以用空格代替，执行删除操作后，问最长的字符串

思路：记录a,b字符的前缀和，然后枚举分界点即可

代码如下：

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
using namespace std;
int suma[5005];
int sumb[5005];
char str[5005];
int main()
{
    scanf("%s",str+1);
    int ans=strlen(str+1);
    for(int i=1;i<=ans;i++)
    {
        suma[i]=suma[i-1]+(str[i]=='a');
        sumb[i]=sumb[i-1]+(str[i]=='b');
    }
    int MAX=0;
    for(int i=1;i<=ans;i++)
        for(int k=i+1;k<=ans;k++)
        {
            MAX=max(MAX,suma[i]/*前面*/+(sumb[k]-sumb[i-1])/*中间*/+(suma[ans]-suma[k-1])/*后面*/);
        }
    if(ans==1)//特判只有一个字母的情况
        cout<<1<<endl;
    else
        cout<<MAX<<endl;
    return 0;
}