/*
ID: philipp17
PROG: beads
LANG: C++                 
*/
/* LANG can be C++11 or C++14 for those more recent releases */
#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>

using namespace std;

enum Colour{ red, blue, white };

int main() {
    ofstream fout ("beads.out");
    ifstream fin ("beads.in");

    int n;
    string s;
    
    fin >> n >> s;

    string doubleNecklace = s.append(s);

    Colour lastBead = white, prewhiteBead = white;
    int currentLength = 0, redLength = 0, blueLength = 0, longestChain = 0, preWhiteLength = 0, inbetweenWhiteLength = 0;

    // The most intricate scenario is the following scenario:
    // white - red - white - blue - white
    // or equivalently:
    // white - blue - white - red - white

    // When white beads are enclosed by beads of the same colour we regard the beads as those colour


    for(const char& bead : doubleNecklace){
        if(bead == 'w'){
            if(lastBead == white){
                currentLength++;
            } else if(lastBead == red){
                prewhiteBead = red;
                redLength = currentLength;
                currentLength = 1;
            } else{ // Last bead is blue
                prewhiteBead = blue;
                blueLength = currentLength;
                currentLength = 1;
            }
            longestChain = max(longestChain, currentLength + redLength + blueLength + prewhiteBead + inbetweenWhiteLength);
            lastBead = white;

        } else if(bead == 'r'){
            if(lastBead == red){
                currentLength++;
                longestChain = max(longestChain, currentLength + preWhiteLength + blueLength + inbetweenWhiteLength);
            } else if(lastBead == blue){
                longestChain = max(longestChain, currentLength + redLength + preWhiteLength + inbetweenWhiteLength);
                blueLength = currentLength;
                redLength = 0;
                currentLength = 1;
                preWhiteLength = inbetweenWhiteLength;
                inbetweenWhiteLength = 0;
            } else{ // Last bead is white
                if(prewhiteBead == red){
                    currentLength += redLength + 1;
                    redLength = 0;
                    longestChain = max(longestChain, currentLength + preWhiteLength + blueLength + inbetweenWhiteLength);
                } else{
                    longestChain = max(longestChain, currentLength + blueLength + redLength + preWhiteLength + inbetweenWhiteLength);
                    preWhiteLength = inbetweenWhiteLength;
                    inbetweenWhiteLength = currentLength;
                    redLength = 0;
                    currentLength = 1;
                }
            }
            lastBead = red;

        } else if(bead == 'b'){
            if(lastBead == blue){
                currentLength++;
                longestChain = max(longestChain, currentLength + redLength + preWhiteLength + inbetweenWhiteLength);
            } else if(lastBead == red){
                longestChain = max(longestChain, currentLength + blueLength + preWhiteLength + inbetweenWhiteLength);
                redLength = currentLength;
                blueLength = 0;
                currentLength = 1;
                preWhiteLength = inbetweenWhiteLength;
                inbetweenWhiteLength = 0;
            } else{ // Last bead is white
                if(prewhiteBead == blue){
                    currentLength += blueLength + 1;
                    blueLength = 0;
                    longestChain = max(longestChain, currentLength + redLength + preWhiteLength + inbetweenWhiteLength);
                } else{
                    longestChain = max(longestChain, currentLength + blueLength + redLength + preWhiteLength + inbetweenWhiteLength);
                    preWhiteLength = inbetweenWhiteLength;
                    inbetweenWhiteLength = currentLength;
                    blueLength = 0;
                    currentLength = 1;
                }
            }
            lastBead = blue;

        } else{
            cout << "unexpected input" << endl;
            return 0;
        }
        // cout << bead << " CurrentLength: " << currentLength << " RedLength: " << redLength << " BlueLength: " << blueLength << " Prewhitelength: " << preWhiteLength << " Inbetweenwhite: " << inbetweenWhiteLength << " LongestChain: " << longestChain << endl;
    }

    fout << min(longestChain, int(s.size()) / 2) << endl;

    return 0;
}