#include <iostream>
#include <queue>
#include <vector>
#include <cstring>
using namespace std;
int n;
string a;
int memo[50000][4][4][4][4];
int f(int at, int l1,int l2,int r1,int r2){
    if(at>=n){
        return 0;
    }
    if(memo[at][l1][l2][r1][r2] != -1 ){
        return memo[at][l1][l2][r1][r2];
    }
    int res= -1;
    int levo = 0, desno = 0;
    vector<bool> visited(4, false);
    visited[l1] = true;
    visited[l2] = true;
    int colour;
    if(a[at] == 'R'){
        colour = 1;
    }
    if(a[at] == 'Y'){
        colour = 2 ;
    }
    if(a[at] =='G'){
        colour = 3;
    }
    visited[colour] = true;
    levo = f(at+1,colour,l1,r1,r2)+visited[1]+visited[2]+visited[3];
    visited[1]  = false;
    visited[2]  = false;
    visited[3]  = false;

    visited[r1] = true;
    visited[r2]= true;
    visited[colour] = true;
    desno  = f(at+1,l1,l2,colour,r1)+visited[1]+visited[2]+visited[3];
    res = max(levo,desno);
    return memo[at][l1][l2][r1][r2] =res;

}
int main() {
    cin >> n;
    cin >> a;
    memset(memo,-1,sizeof(memo));
    cout << f(0,0,0,0,0);
}