#include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <queue>
#include <set>
#include <unordered_set>
#include <complex>
#include <list>
#include <cassert>
#include <chrono>
#include <random>
#include <stack>
#include <iomanip>
#include <fstream>
using namespace std;
#define endl "\n"
// #define int long long
const int INF = 1e9+7;
const int MOD = 1e9+7;
int n, sol = 0, asd = 1;
string s;
int check(char a, char b, char c){
unordered_set<char> st;
st.insert(a);
st.insert(b);
st.insert(c);
return (int)st.size();
}
void perm(int i, vector<char> a, vector<char> b){
if(i == n){
int cnt = 0;
for(int i = 0; i < (int)a.size(); i++){
if(i == 0){
cnt++;
} else if(i == 1){
if(a[i-1] == a[i]) cnt += 1;
else cnt += 2;
} else {
cnt += check(a[i], a[i-1], a[i-2]);
}
}
for(int i = 0; i < (int)b.size(); i++){
if(i == 0){
cnt++;
} else if(i == 1){
if(b[i-1] == b[i]) cnt += 1;
else cnt += 2;
} else {
cnt += check(b[i], b[i-1], b[i-2]);
}
}
sol = max(sol, cnt);
return;
}
a.push_back(s[i]);
perm(i+1, a, b);
a.pop_back();
b.push_back(s[i]);
perm(i+1, a, b);
b.pop_back();
}
void solve(){
cin >> n >> s;
perm(0, {}, {});
cout << sol << endl;
}
int32_t main(){
ios_base::sync_with_stdio(false); cin.tie(nullptr);
int t = 1;
// cin >> t;
while(t--) solve();
return 0;
}
