#include <iostream>
#include <vector>
#include <string>
using namespace std;
const int abc = 11, inf = 1e9 + 5;
void upd(int& a, const int& b) { a = min(a, b); }
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int n; cin >> n;
string s;
cin >> s;
int cnte = 0;
vector<int> t; vector<bool> u;
for (int i = 0; i < n; i++)
{
if (s[i] == 'e') cnte++;
else
{
t.push_back(s[i] - 'a');
u.push_back(i && s[i - 1] == 'e');
}
//if (s[i] == 'e') cout << 2;
//else cout << (int)u.back();
} //cout << endl;
t.push_back(abc - 1), u.push_back(false);
int m = t.size();
vector<vector<int> > p(m, vector<int>(abc, inf));
vector<vector<vector<int> > > q(m, vector<vector<int> >(abc, vector<int>(abc, inf)));
p[0][t[0]] = q[0][t[0]][t[0]] = 0;
for (int a = 0; a < m - 1; a++)
{
for (int c = 0; c < abc; c++)
{
if (!u[a] && c != t[a]) upd(p[a + 1][c], p[a][c]);
upd(p[a + 1][c], p[a][t[a]] + 2);
if (c != t[a]) upd(p[a + 1][c], q[a][t[a]][c]);
upd(p[a + 1][c], q[a][t[a]][t[a]] + 2);
for (int d = 0; d < abc; d++)
{
if (c != t[a]) upd(q[a + 1][c][d], p[a][c] + 3);
upd(q[a + 1][c][d], p[a][t[a]] + 5);
if (c != t[a] && d != t[a]) upd(q[a + 1][c][d], q[a][c][d] + 1);
if (c != t[a]) upd(q[a + 1][c][d], q[a][c][t[a]] + 3);
if (d != t[a]) upd(q[a + 1][c][d], q[a][t[a]][d] + 3);
upd(q[a + 1][c][d], q[a][t[a]][t[a]] + 5);
}
}
}
cout << p[m - 1][abc - 1] - 2 + cnte * 2 << "\n";
return 0;
}
