#include "bits/stdc++.h"
using namespace std;
int INF = 1e9;
int main() {
ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
clock_t startTime = clock();
int n;
string s;
cin >> n >> s;
vector<vector<int>> pos(150);
vector<int> not_e;
for (int i = 0; i < n; i++) {
pos[s[i]].emplace_back(i);
if (s[i] != 'e') {
not_e.emplace_back(i);
}
}
if (pos['e'].empty()) {
cout << 0;
return 0;
}
auto cnt = [&](int l, int r, char x) {
return upper_bound(pos[x].begin(), pos[x].end(), r) - lower_bound(pos[x].begin(), pos[x].end(), l);
};
vector<vector<int>> dist(n, vector<int>(n, INF));
auto dist_calc = [&](int l, int r) {
int ans = INF;
for (char x = 'a'; x <= 'z'; x++) {
if (x == 'e' or pos[x].empty() or pos[x].back() < r) continue;
int first = *lower_bound(pos[x].begin(), pos[x].end(), r);
int now = cnt(l + 1, first, x) * 2;
now += first - r;
ans = min(ans, now);
}
return min(ans, dist[l][r]);
};
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
dist[i][j] = dist_calc(i, j);
}
}
for (int k = 0; k < n; k++) {
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
if (i <= k and k <= j) {
dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
}
}
}
}
vector<vector<int>> dp(pos['e'].size(), vector<int>(pos['e'].size(), INF));
for (int i = 0; i < dp.size(); i++) {
// birinchi i ta 'e' ni o'chirish
for (int j = 0; j <= i; j++) {
// birinchi i ta 'e' ni o'chirib, j-'e' da to'xtash
if (j == 0) {
int now = dist_calc(0, pos['e'][i]);
// orasida hammasi bilan yurib chiqish
now += pos['e'][i] - pos['e'][0];
// 'e' larni o'chirish
now += i + 1;
dp[i][j] = now;
continue;
// bu qismi to'g'ri
}
for (int k = 0; k < j; k++) {
int now = dp[j - 1][k] + dist_calc(*lower_bound(not_e.begin(), not_e.end(), pos['e'][k]), pos['e'][i]);
now += pos['e'][i] - pos['e'][j];
now += i - j + 1;
dp[i][j] = min(dp[i][j], now);
}
}
}
// i = 2, j = 2, k = 0
cout << *min_element(dp.back().begin(), dp.back().end());
#ifdef sunnitov
cerr << "\nTime: " << (int)((double)(clock() - startTime) / CLOCKS_PER_SEC * 1000);
#endif
}
/*
chefeddiefedjeffeachbigagedegghehad - 0
chefeddiefedjeffeachbigagedegghehad - 0
*/
