#include <bits/stdc++.h>
using namespace std;
// dbg
#ifdef LOCAL
#include "../dbg.h"
#else
#define dbg(...)
#endif
// typedefs
using ll = long long;
#define LONG_LONGS
#ifdef LONG_LONGS
#define int ll
const int inf = (int)1e18;
#else
const int inf = int(1e9);
#endif
using vi = vector<int>;
using vvi = vector<vi>;
using p2 = pair<int, int>;
using vp2 = vector<p2>;
using vvp2 = vector<vp2>;
#define rep(i, high) for (int i = 0; i < high; i++)
#define repp(i, low, high) for (int i = low; i < high; i++)
#define repe(i, container) for (auto& i : container)
#define per(i, high) for (int i = high - 1; i >= 0; i--)
#define perr(i, high, low) for (int i = high - 1; i >= low; i--)
// Builtins
#define clz(x) __builtin_clz(x)
#define popcount(x) __builtin_popcountll(x)
// Fast I/O
inline void fast() {
ios::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
}
void readinput() {} // Recursion base case
template <typename T, typename... Args>
void readinput(T& arg, Args&... args) {
read(arg);
readinput(args...);
}
#define dread(type, ...) \
type __VA_ARGS__; \
readinput(__VA_ARGS__);
template <typename T>
istream& operator>>(istream& is, vector<T>& v) {
repe(u, v) read(u);
return is;
}
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define setcontains(set, x) (set.find(x) != set.end())
#define sz(container) ((int)container.size())
vector<p2> dirs = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
// time and rng
auto Start = chrono::high_resolution_clock::now();
void resettimer() {
Start = chrono::high_resolution_clock::now();
}
int elapsedmillis() {
return chrono::duration_cast<chrono::milliseconds>(
chrono::high_resolution_clock::now() - Start
)
.count();
}
random_device rd;
mt19937 rng(rd());
template <typename T, typename U>
inline int randint(T lo, U hi) {
return uniform_int_distribution<int>((int)lo, (int)hi)(rng);
} // [lo,hi]
template <typename T>
inline T randel(vector<T>& v) {
return v[uniform_int_distribution<int>(int(0), int(v.size()) - int(1))(rng)];
} // [lo,hi]
const int N = 5050;
int dp[N][N];
int nxt_ne[N];
int nxt[N][20];
int num_es[N];
vi e_pos;
int es = 0;
int dpf(int a, int b) {
if (b == es)
return 0;
int& ans = dp[a][b];
if (ans != -1)
return dp[a][b];
ans = inf;
if (a >= e_pos[b]) {
ans = a - e_pos[b];
ans += dpf(nxt_ne[e_pos[b]], num_es[a]);
}
rep(i, 10) {
if (i + 'a' == 'e')
continue;
int n = nxt[a][i];
if (n == -1)
continue;
ans = min(ans, 2 + dpf(n, b));
}
return ans;
}
signed main() {
fast();
memset(dp, -1, sizeof(dp));
memset(nxt, -1, sizeof(nxt));
memset(num_es, 0, sizeof(num_es));
int n;
string line;
cin >> n >> line;
int prev[20];
int preve = 0;
rep(i, sz(line)) {
int chr = line[i] - 'a';
repp(j, prev[chr], i) nxt[j][chr] = i;
prev[chr] = i;
if (chr + 'a' == 'e') {
e_pos.push_back(i);
es++;
} else {
repp(j, preve, i) nxt_ne[j] = i;
preve = i;
}
num_es[i] = es;
num_es[i + 1] = es;
}
// dbg(num_es, es);
dbg(nxt, nxt_ne);
cout << dpf(0, 0) + es;
return 0;
}
