#include <bits/stdc++.h>
using namespace std;
const int N = 70005;
const int INF = 0x3f3f3f3f;
int n;
int cost;
int a[N];
int b[N][11];
int f[N][11];
bool flag[N];
string s;
int main() {
ios::sync_with_stdio(false);
cin >> n >> s;
string t = s; s.clear();
flag[0] = 1;
for (int i = 0; i < n; ++i) {
if (t[i] == 'e') flag[s.size()] = 1, cost += 2;
else s.push_back(t[i]);
}
n = s.size();
int cur = n;
for (int i = n - 1; i >= 0; --i) {
a[i] = cur; if (flag[i]) cur = i;
}
for (int i = 0; i < 10; ++i) {
int cur = n;
for (int j = n - 1; j >= 0; --j) {
b[j][i] = cur;
if (s[j] - 'a' == i) cur = j;
}
}
memset(f, INF, sizeof f);
int res = INF; f[0][10] = 0;
// cout << s << '\n';
for (int i = 0; i < n; ++i) {
for (int j = 0; j <= 10; ++j) {
if (f[i][j] == INF) continue;
// cout << i << ' ' << j << ' ' << f[i][j] << '\n';
if (j == 10) {
if (a[i] == n) res = min(res, f[i][j]);
}
else {
if (a[b[i][j]] == n) res = min(res, f[i][j]);
}
for (int k = 0; k < 10; ++k) {
int x = b[i][k];
if (x == n) continue;
int y;
if (j == 10) y = a[i];
else {
if (x < b[i][j]) continue;
y = a[b[i][j]];
}
if (y >= x) f[x][10] = min(f[x][10], f[i][j] + 2);
else {
f[y][k] = min(f[y][k], f[i][j] + 2 + x - y);
}
}
}
}
cout << res + cost;
}
