#include <bits/stdc++.h>
using namespace std;
const long long INFll = (long long) 1e18 + 10;
const int INFii = (int) 1e9 + 10;
typedef long long ll;
typedef int ii;
typedef long double dbl;
#define endl '\n'
#define sc second
#define fr first
#define mp make_pair
#define pb push_back
#define all(x) x.begin(), x.end()
#define maxn 5050
ii n, a[maxn], dp[maxn][maxn], mark[maxn][maxn], px[maxn][20], pse[maxn];
ii sol(ii i, ii j) {
if(j == n+1) return 0;
if(i > n) return INFii;
if(mark[i][j]) return dp[i][j];
mark[i][j] = 1;
if(a[j] != 'e'-'a') return dp[i][j] = sol(i,j+1);
ii ans = INFii;
for(ii c = 0; c <= 'j'-'a'; c++) {
if(c == 'e'-'a') continue;
if(px[i+1][c] != 0) ans = min(ans, sol(px[i+1][c],j)+2); //i+1 para nao contar com ele mesmo
}
if(j <= i) {
ans = min(ans, sol(j+1,i+1) + (i-j) + (pse[i]-pse[j-1]));
}
return dp[i][j] = ans;
}
int main() {
ios::sync_with_stdio(false); cin.tie(0);
// freopen("in.in", "r", stdin);
//freopen("out.out", "w", stdout);
string s;
cin >> n >> s;
for(ii i = 1; i <= n; i++) {
pse[i] = pse[i-1];
if(s[i-1] == 'e') {
pse[i]++;
}
a[i] = s[i-1]-'a';
}
for(ii i = n; i >= 1; i--) {
for(ii c = 0; c <= 'j'-'a'; c++) {
px[i][c] = px[i+1][c];
}
px[i][a[i]] = i;
}
for(ii i = 1; i <= n; i++) {
for(ii c = 0; c <= 'j'-'a'; c++) {
//cout << i << " " << (char) (c+'a') << " == " << px[i][c] << endl;
}
}
cout << sol(1,1) << endl;
}
