A chain contains N red, white, or blue beads (3 b b b r b r b b r r 12 rbbr b r rbr

• A chain contains N red, white, or blue beads (3<=N<=500), arranged at random. Figures 1 and 2 show examples for N=29 (r : red bead, b : blue bead, w : white bead).

  
  

  

  Figure 1 Figure 2

  
  

  The numbers 1 and 2 refer to the first and second beads, respectively. Figure 1 shows a chain with blue and red beads only and will be given in the data as follows:

  brbrrrbbbrrrrrbrrbbrbbbbrrrrb

  Suppose you break the chain at some point and lay it out in a straight line. You collect beads of the same color from one end until you reach a bead of a different colour. You repeat this from the other end, noting that the beads collected now could be of a different colour from those collected previously.

  
  

  Some chains may contain white beads as shown in Figure 2. When collecting beads, a white bead encountered may be treated as either red or blue.

  
  

  Write a program to determine the point where a given chain should be broken so that the most number of beads can be collected.

  
  

  For example, for the chain in Figure 1, 8 beads can be collected, with the breaking point either between bead 9 and bead 10 or between bead 24 and bead 25.

  Input: The first line contains N and the second line contains N beads (r, b or w). For example,

  29

  brbrrrbbbrrrrrbrrbbrbbbbrrrrb

  
  

  Output: The maximum of number of beads that can be collected from the given chain. For the chain in Figure 1, you should output

  
  

  8

  
  

  Data must be read from the file input.txt and output sent to the file output.txt.

b b b r b r b b r r 12 rbbr b r rbr Figure 1 r r r DDD b b b r W r b r W b b b 1 2 brrb r rrw Figure 2 b b r W LDD b b r r