#include <iostream>
#include <vector>
using namespace std;
int dp[50000][4][4][4][4];

int main()
{
    int n;
    cin >> n;
    string s;
    cin >> s;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < 4; j++) {
            for(int k = 0; k < 4; k++) {
                for(int x = 0; x < 4; x++) {
                    for(int y = 0; y < 4; y++) {
                        dp[i][j][k][x][y] = -2e9;
                    }
                }
            }
        }
    }
    dp[0][0][0][0][0] = 0;
    int color = 0;
    int cost;
    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++) {
                        vector<bool> visited(4, false);
                        if(s[i] == 'R') color = 1;
                        if(s[i] == 'Y') color = 2;
                        if(s[i] == 'G') color = 3;
                        visited[color] = true;
                        visited[l1] = true;
                        visited[l2] = true;
                        cost = visited[1] + visited[2] + visited[3];
                        dp[i + 1][color][l1][r1][r2] = max(dp[i + 1][color][l1][r1][r2],
                                                           dp[i][l1][l2][r1][r2] + cost);
                        visited[1] = false;
                        visited[2] = false;
                        visited[3] = false;
                        visited[color] = true;
                        visited[r1] = true;
                        visited[r2] = true;
                        cost = visited[1] + visited[2] + visited[3];
                        dp[i + 1][l1][l2][color][r1] = max(dp[i + 1][l1][l2][color][r1],
                                                           dp[i][l1][l2][r1][r2] + cost);
                        
                        
                    }
                }
            }
        }
    }
    int result = 0;
    
    for(int i = 0; i <= n; i++) {
        for(int j = 0; j < 4; j++) {
            for(int k = 0; k < 4; k++) {
                for(int x = 0; x < 4; x++) {
                    for(int y = 0; y < 4; y++) {
                        result = max(result, dp[i][j][k][x][y]);
                    }
                }
            }
        }
    }
    cout << result << endl;
    return 0;
}