// #pragma GCC target ("avx,avx2,fma")
// #pragma GCC optimize ("Ofast,inline") // O1 - O2 - O3 - Os - Ofast
// #pragma GCC optimize ("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (int i = (a); i < (b); ++i)
#define per(i, a, b) for (int i = (b - 1); i >= (a); --i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) x.size()
#define pb push_back
#define debug(x) cout << #x << " = " << x << endl
#define umap unordered_map
#define uset unordered_set
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef vector<pll> vpll;
const int INF = 1'000'000'007;
vi lets[130], skip_e;
int n, cnt = 0, memo[5001][5001];
string str;
int dp(int pos, int taken) {
if (taken == cnt) return 0;
int &ans = memo[pos][taken];
if (ans != -1) return memo[pos][taken];
ans = INF;
if (lets['e'][taken] <= pos) {
int nxt_taken = upper_bound(all(lets['e']), pos) - lets['e'].begin();
int nxt_pos = *upper_bound(all(skip_e), lets['e'][taken]);
//cout << "pos = " << pos << " taken = " << taken << " nxt_taken = " << nxt_taken << " nxt_pos = " << nxt_pos << endl;
ans = (pos - lets['e'][taken]) + dp(nxt_pos, nxt_taken);
}
rep(i, 'a', 'k') {
if (i == 'e') continue;
vi &vec = lets[i];
auto it = upper_bound(all(vec), pos);
if (it != vec.end()) ans = min(ans, 2 + dp(*it, taken));
}
//cout << "pos = " << pos << " taken = " << taken << " ans = " << ans << endl;
return ans;
}
int main() {
cin.tie(0)->sync_with_stdio(0);
cin.exceptions(cin.failbit);
memset(memo, -1, sizeof(memo));
cin >> n >> str;
rep(i, 0, n) {
lets[str[i]].pb(i);
if (str[i] != 'e') skip_e.pb(i);
}
cnt = sz(lets['e']);
cout << dp(0, 0) + cnt << endl;
return 0;
}
