// Zende bad Shoma nasime faghat !
#include <bits/stdc++.h>
#define pb push_back
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define debug(x) cerr << #x << " : " << x << '\n'
using namespace std;
typedef long long ll;
typedef long double ld;
typedef string str;
typedef pair<ll, ll> pll;
const ll Mod = 1000000007LL;
const int N = 5e3 + 10;
const int Inf = 1e9;
const ll Log = 30;
str s;
int dp[N][N];
int nx[N][12], nxe[N], ps[N], ps2[N];
int main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
ll n;
cin >> n >> s;
memset(nx, -1, sizeof nx);
nxe[n - 1] = n - 1;
for(int i = n - 2; i >= 0; i--){
for(int j = 0; j < 10; j++) nx[i][j] = nx[i + 1][j];
nx[i][s[i + 1] - 'a'] = i + 1;
nxe[i] = (s[i] == 'e' ? nxe[i + 1] : i);
}
vector<int> E;
ps2[0] = 1;
for(int i = 1; i < n; i++){
if(s[i] == 'e') E.pb(i);
ps[i] = ps[i - 1] + (s[i] == 'e' ? 1 : 0);
ps2[i] = ps2[i - 1] + (s[i] == 'e' ? 0 : 1);
}
int ce = E.size();
memset(dp, 31, sizeof dp);
dp[0][0] = 0;
for(int j = 0; j < ce; j++){
for(int i = 0; i < n; i++){
if(s[i] == 'e') continue;
for(int c = 0; c < 10; c++){
if(nx[i][c] != -1) dp[nx[i][c]][j] = min(dp[nx[i][c]][j], dp[i][j] + 2);
}
if(E[j] < i){
dp[ nxe[E[j]] ][ps[i]] = min(dp[ nxe[E[j]] ][ps[i]], dp[i][j] + ps2[i] - ps2[nxe[E[j]]]);
}
}
}
int ans = Inf;
for(int i = 0; i < n; i++){
ans = min(ans, dp[i][ce] + ce + ce);
}
//debug(dp[3][2]);
//debug(nx[3][5]);
//debug(dp[9][2]);
cout << ans << '\n';
return 0;
}
