// And you curse yourself for things you never done
#include<bits/stdc++.h>
#define F first
#define S second
#define PB push_back
#define sz(s) int((s).size())
#define bit(n,k) (((n)>>(k))&1)
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int maxn = 5010, mod = 1e9 + 7, inf = 1e9 + 10;
int dp[maxn][maxn];
int nxt[maxn][10], lst[10];
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie();
int n;
cin >> n;
string _s, s;
cin >> _s;
int ans = 0;
vector<int> poses;
for(int i = 0; i < n; i++){
if(_s[i] == 'e')
ans+= 2;
if(_s[i] == 'e' && _s[i + 1] != 'e')
poses.PB(sz(s));
if(_s[i] != 'e')
s+= _s[i];
}
memset(lst, -1, sizeof lst);
memset(nxt, -1, sizeof nxt);
n = sz(s);
for(int i = n-1; i >= 0; i--){
memcpy(nxt[i], lst, sizeof lst);
int id = (s[i] - 'a') - (s[i] > 'e');
lst[id] = i;
}
for(int i = sz(poses)-1; i >= 0; i--){
int pt = sz(poses)-1;
for(int j = n-1; j >= 0; j--){
dp[i][j] = inf;
if(pt >= i)
dp[i][j] = j - poses[i] + dp[pt + 1][poses[i]];
for(int k = 0; k < 9; k++)
if(nxt[j][k] != -1)
dp[i][j] = min(dp[i][j], 2 + dp[i][nxt[j][k]]);
if(poses[pt] == j)
pt--;
}
}
ans+= dp[0][0];
return cout << ans << "\n", 0;
}
