C++ :

#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    char s[700],c=0;
    int n,i,temp=0,num=0,w=0,ans=0;
    cin>>n>>s;
    memcpy(s+n,s,n);//copy
    for (i=0;i<n*2;i++)
        if (s[i]=='w') num++,w++; //如果是w，把它视为当前颜色，并计数，下面有用
        else if (s[i]==c) num++,w=0;//是当前连续的颜色，计数，w清零
        else //不是的话
        {
            if (temp+num>ans) ans=temp+num;//做一次比较，记录ans
            temp=num-w;num=w+1;w=0;c=s[i];//连续的颜色改变，就开始用temp记录，比如wwwbrwrbww,生成wwwbrwrbwwwwwbrwrbww；
                                           //  一开始是w那么w++;在s【3】时改变temp=0；因为没别的颜色。w就看作b；b=4；
                                           //下一次颜色改变，temp=4，num=1；因为b后没有w这时连续颜色为r有w；以此类推；
                                           //这样子不断重复，其实就是过滤w，只有r，b只要求一个点左边连续的rrrbbbb呀就行在改变点
                                           //断开就可以了；当然会有重复，比如wwwwbbbbrrrr，这是就输出n
                                           //最后的语句就是判断
        }
    if (temp+num>ans) ans=temp+num;//
    cout<<(ans>n?n:ans)<<endl;//
    return 0;
}

Pascal :

program beads;
var s:ansistring;
    bl,rl,br,rr:array[0..351]of integer;
    i,n,max,temp:integer;
begin
  readln(n);
  readln(s);
  bl[0]:=0;
  rl[0]:=0;
  for i:=1 to n do     
  begin
    case s[i] of
      'r':
      begin
        rl[i]:=rl[i-1]+1;
        bl[i]:=0;
      end;
      'b':
      begin
        bl[i]:=bl[i-1]+1;
        rl[i]:=0;
      end;
      'w':
      begin
        bl[i]:=bl[i-1]+1;
        rl[i]:=rl[i-1]+1;
      end;
    end;
  end;
  bl[0]:=bl[n];
  rl[0]:=rl[n];
  for i:=1 to n do    
  begin
    case s[i] of
      'r':
      begin
        rl[i]:=rl[i-1]+1;
        bl[i]:=0;
      end;
      'b':
      begin
        bl[i]:=bl[i-1]+1;
        rl[i]:=0;
      end;
      'w':
      begin
        bl[i]:=bl[i-1]+1;
        rl[i]:=rl[i-1]+1;
      end;
    end;
    if rl[i]>n then rl[i]:=n;
    if bl[i]>n then bl[i]:=n;
  end;
  br[n+1]:=0;
  rr[n+1]:=0;
  for i:=n downto 1 do 
  begin
    case s[i] of
      'r':
      begin
        rr[i]:=rr[i+1]+1;
        br[i]:=0;
      end;
      'b':
      begin
        br[i]:=br[i+1]+1;
        rr[i]:=0;
      end;
      'w':
      begin
        br[i]:=br[i+1]+1;
        rr[i]:=rr[i+1]+1;
      end;
    end;
  end;
  br[n+1]:=br[1];
  rr[n+1]:=rr[1];
  for i:=n downto 1 do 
  begin
    case s[i] of
      'r':
      begin
        rr[i]:=rr[i+1]+1;
        br[i]:=0;
      end;
      'b':
      begin
        br[i]:=br[i+1]+1;
        rr[i]:=0;
      end;
      'w':
      begin
        br[i]:=br[i+1]+1;
        rr[i]:=rr[i+1]+1;
      end;
    end;
    if rr[i]>n then rr[i]:=n;
    if br[i]>n then br[i]:=n;
  end;
  bl[n+1]:=bl[1];
  br[n+1]:=br[1];
  rl[n+1]:=rl[1];
  rr[n+1]:=rr[1];
  max:=-1;
  for i:=1 to n do
  begin
    if bl[i]>rl[i]then temp:=bl[i] else temp:=rl[i];
    if br[i+1]>rr[i+1]then inc(temp,br[i+1]) else inc(temp,rr[i+1]);
    if temp>max then max:=temp;
    if max>n then max:=n;
  end;
  writeln(max);
end.