#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T> V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> > Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T> mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }

/*
 <url:http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=2767>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

ll solve(){
    ll res = 0;
    ll N; cin >> N;
    string S; cin >> S;
    vector<int> alpha;
    for(int i = 0; i < 26;i++){
        int x = (int)count(S.begin(),S.end(),'a'+i);
        if(x == 0) continue;
        alpha.push_back(x);
    }
    sort(alpha.begin(),alpha.end());
    ll len0 = 0, len1 = 0;
    for(auto v:alpha){
        if(v == 1) len0 += 1;
        else len0 += 3;
    }
    len0 += alpha.size()-1;
    
    for(int x = 1; x <= 9; x++){
        int y = (int)count(alpha.begin(),alpha.end(),x);
        if(y == 0) continue;
        if(x == 1){
            len1 += (2*y-1);
        }else{
            if(y == 1){
                len1 += 3*y;
            }else{
                len1 += (4+2*y-1);
            }
        }
    }
    alpha.erase(unique(alpha.begin(),alpha.end()),alpha.end());
    len1 += alpha.size()-1;
    res = min(len0,len1);
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    cout << solve() << endl;
    return 0;
}

