#include <iostream>
#include <algorithm>
#include <vector>
#include <cstring>
#include <set>
using namespace std;
const int maxn = 55000;
const int INF = 2e9;

string s;
int n;

int score(int a, int b, int c) {
    vector<bool> visited(4, false);
    visited[a] = true;
    visited[b] = true;
    visited[c] = true;

    return visited[1] + visited[2] + visited[3];
}
int color(char c) {
    if(c == 'R') return 1;
    if(c == 'G') return 2;
    return 3;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin >> n >> s;
    int dp[n + 1][4][4][4][4];

    for(int i = 0; i <= n; i++) {
        for(int L1 = 0; L1 <= 3; L1++) {
            for(int L2 = 0; L2 <= 3; L2++) {
                for(int R1 = 0; R1 <= 3; R1++) {
                    for(int R2 = 0; R2 <= 3; R2++) {
                        dp[i][L1][L2][R1][R2] = -INF;
                    }
                }
            }
        }
    }


    dp[0][0][0][0][0] = 0;

    int res = 0;
    for(int at = 0; at < n; at++) {
        for(int L1 = 0; L1 <= 3; L1++) {
            for(int L2 = 0; L2 <= 3; L2++) {
                for(int R1 = 0; R1 <= 3; R1++) {
                    for(int R2 = 0; R2 <= 3; R2++) {
                        int now = at;
                        int next = at + 1;

                        int colour = color(s[at]);
                        int cost = score(L1, L2, colour);
                        dp[next][colour][L1][R1][R2] = max(dp[now][L1][L2][R1][R2] + cost, dp[next][colour][L1][R1][R2]);

                        cost = score(R1, R2, colour);
                        dp[next][L1][L2][colour][R1] = max(dp[now][L1][L2][R1][R2] + cost, dp[next][L1][L2][colour][R1]);


                    }
                }
            }
        }
    }

    for(int L1 = 0; L1 <= 3; L1++) {
        for(int L2 = 0; L2 <= 3; L2++) {
            for(int R1 = 0; R1 <= 3; R1++) {
                for(int R2 = 0; R2 <= 3; R2++) {
                    res = max(res, dp[n][L1][L2][R1][R2]);
                }
            }
        }
    }

    cout << res << endl;
    return 0;
}