#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
void solve(int test_case)
{
ll n; cin >> n;
string s; cin >> s;
s = "$" + s;
ll nxt[n+5][10];
memset(nxt,0x3f,sizeof nxt);
array<ll,10> closest;
closest.fill(inf2);
rev(i,n,1){
rep(j,10){
nxt[i][j] = closest[j];
}
closest[s[i]-'a'] = i;
}
vector<ll> p(n+5);
rep1(i,n) p[i] = p[i-1]+(s[i] == 'e');
ll m = p[n];
ll dp[n+5][m+5];
memset(dp,0x3f,sizeof dp);
dp[1][0] = 0;
rep1(i,n){
rep(j,m+1){
rep(ch,10){
if(ch == 4) conts;
// if(dp[i][j]) conts;
ll k = nxt[i][ch];
if(k > n) conts;
ll cnt = p[k]-p[i];
for(int x = i; x <= min(nxt[i][4],k); ++x){
amin(dp[x][p[k]],dp[i][j]+1+cnt*2+k-x);
}
if(nxt[i][4]+1 <= k){
ll x = nxt[i][4]+1;
ll two_cnt = cnt-1;
ll one_cnt = k-(x-1)+1-two_cnt;
amin(dp[x][p[k]],dp[i][j]+1+cnt*two_cnt+one_cnt);
}
}
}
}
ll ans = inf2;
rep1(i,n){
amin(ans,dp[i][m]);
}
ans += m-1;
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
