#include 
    #include 
    #include 
    #include 
    using namespace std;
    int n;
    string a;
    int memo[2][4][4][4][4];
    int main() {
        cin >> n;
        cin >> a;
        for(int i = 0; i < 2; i++) {
            for(int l1 = 0; l1 < 4; l1++) {
                for(int l2 = 0; l2 < 4; l2++) {
                    for(int r1 = 0; r1 < 4; r1++) {
                        for(int r2 = 0; r2 < 4; r2++) {
                            memo[i][l1][l2][r1][r2] = -2e9;
                        }
                    }
                }
            }
        }

        memo[0][0][0][0][0] = 0;
        
        for(int i = 0; i < n; i++) {
            for(int l1 = 0; l1 < 4; l1++) {
                for(int l2 = 0; l2 < 4; l2++) {
                    for(int r1 = 0; r1 < 4; r1++) {
                        for(int r2 = 0; r2 < 4; r2++) {
                            int now = i % 2;
                            int next = 1 - now;
                            vector visited(4, false);
                            int color;
                            if(a[i] == 'R') {
                                color = 1;
                            }
                            else if(a[i] == 'Y') {
                                color = 2;
                            }
                            else {
                                color = 3;
                            }
                            visited[color] = true;
                            visited[l1] = true;
                            visited[l2] = true;
                            int score = visited[1] + visited[2] + visited[3];
                            
                            memo[next][color][l1][r1][r2] = max(memo[next][color][l1][r1][r2], memo[now][l1][l2][r1][r2] + score);
                            visited[1] = false;
                            visited[2] = false;
                            visited[3] = false;
                            
                            visited[color] = true;
                            visited[r1] = true;
                            visited[r2] = true;
                            
                            score = visited[1] + visited[2] + visited[3];
                            
                            memo[next][l1][l2][color][r1] = max(memo[next][l1][l2][color][r1], memo[now][l1][l2][r1][r2] + score);
                            
                                                           
                        }
                    }
                }
            }
        }
        
        int result = 0;
        for(int i = 0; i < 2; i++) {
            for(int l1 = 0; l1 < 4; l1++) {
                for(int l2 = 0; l2 < 4; l2++) {
                    for(int r1 = 0; r1 < 4; r1++) {
                        for(int r2 = 0; r2 < 4; r2++) {
                            result = max(result, memo[i][l1][l2][r1][r2]);
                        }
                    }
                }
            }
        }
        cout << result << endl;
        return 0;
    }