#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
#define FOR(i,a,b) for(int i = (a) , _b = (b); i <= _b; ++i)
#define BIT(mask , x) (((mask) >> (x)) & (1))
#define MASK(x) ((LL)(1) << (x))
#define sz(x) (int)(x).size()
#define TIME_USED cerr << "\n Time lapsed : " << 1.0 * clock() / CLOCKS_PER_SEC << "s \n";
template<class T1 , class T2>
bool maximize(T1 &a , T2 b){
if (a < b) return a = b , true; else return false;
}
template<class T1 , class T2>
bool minimize(T1 &a , T2 b){
if (a > b) return a = b , true; else return false;
}
template<class T1 , class T2>
T2 Find(const vector<T1>&data , T2 y){
return upper_bound(data.begin() , data.end() , y) - data.begin();
}
template<class T>
void compress(vector<T>&data){
sort(data.begin() , data.end());
data.resize(unique(data.begin() , data.end()) - data.begin());
}
const int N = (int) 7e4;
const int inf = (int) 1e9;
const int MAXK = (int) 11;
const int const_id = 4;
vector<int> occur[MAXK + 2];
int a[N + 2];
string s;
int n;
int Find_nxt(int c , int x){
int tt = lower_bound(occur[c].begin() , occur[c].end() , x) - occur[c].begin();
--tt;
if (tt == -1) return tt;
return occur[c][tt];
}
//... ARRAY FOR PROCESSING
int dp[N + 2][2] = {};
int rig[N + 2] = {};
int pre[N + 2] = {};
int Get_prefix(int l , int r){
return pre[r] - pre[l - 1];
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0) ; cout.tie(0) ;
#define name "main"
if (fopen(name".inp","r")){
freopen(name".inp","r",stdin);
freopen(name".out","w",stdout);
}
cin >> n >> s;
s = '#' + s;
for(int i = 1; i <= n; ++i) a[i] = (int)s[i] - 'a';
for(int i = 1; i <= n; ++i) occur[a[i]].push_back(i);
//... PRE BUILD
rig[n + 1] = n + 1;
for(int i = n; i >= 1; --i){
if (a[i] == const_id) rig[i] = i; else rig[i] = rig[i + 1];
}
for(int i = 1; i <= n; ++i) pre[i] = pre[i - 1] + (a[i] == const_id);
int start = 1 , ans = 0;
memset(dp , 0x3f , sizeof dp);
dp[start][1] = dp[start][0] = ans;
for(int i = start; i <= n; ++i){
if (a[i] == const_id) continue;
for(int j = 0; j <= MAXK; ++j){
if (j == const_id) continue;
int t = Find_nxt(j , i);
if (t == -1) continue;
int last_ptr = min(rig[t] , i);
minimize(dp[i][0] , dp[t][1] + 2 + Get_prefix(t , i) + i - last_ptr);
}
minimize(dp[i][1] , dp[i][0]);
}
ans = inf;
for(int i = 1; i <= n; ++i) if (pre[i] == pre[n]) minimize(ans , dp[i][1]);
cout << ans;
return 0;
}
