#include <bits/stdc++.h>
typedef long long ll;
using namespace std;
int dp[5050][5050], nxt[10][5050], prv[5050];
vector<int> E, pos;
int main(){
cin.tie(NULL);
ios_base::sync_with_stdio(false);
int n;
string a;
cin >> n >> a;
if (n>5000) {printf("0\n"); return 0;}
string::iterator s = a.begin()-1;
int pt[10] = {0};
E.push_back(0);
for (int i=1;i<=n;i++){
if (s[i]=='e'){
E.push_back(i);
prv[i] = (int)E.size()-1;
}
else{
while(pos.size()<E.size()) pos.push_back(i);
prv[i] = prv[i-1];
for (int j=pt[s[i]-'a'];j<i;j++) nxt[s[i]-'a'][j] = i;
pt[s[i]-'a'] = i;
}
}
for (int j=0;j<10;j++){
for (int i=pt[j];i<=n;i++) nxt[j][i] = 1e9;
//for (int i=1;i<=n;i++) printf("%d ", nxt[j][i]);
//printf("\n");
}
/*for (auto &x:E) printf("%d ", x);
printf("\n");
for (auto &x:pos) printf("%d ", x);
printf("\n");
for (int i=1;i<=n;i++) printf("%d ", prv[i]);
printf("\n");*/
if (E.empty()){
printf("0\n"); return 0;
}
for (int i=0;i<(int)E.size();i++){
fill(dp[i], dp[i]+n+1, 1e9);
}
dp[0][1] = 0;
for (int i=0;i<(int)E.size();i++){
for (int j=1;j<=n;j++){
for (int k=0;k<10;k++){
int idx = nxt[k][j];
if (idx==1e9 || prv[idx]<i) continue;
if (prv[idx]!=i) dp[prv[idx]][pos[i+1]] = min(dp[prv[idx]][pos[i+1]], dp[i][j] + (idx - E[i+1]) + (prv[idx] - i) + 2);
else dp[i][idx] = min(dp[i][idx], dp[i][j] + 2);
}
}
}
//printf("%d\n", nxt[3][pos[0]]);
//printf("%d\n", dp[0][0] + (6 - E[0]));
int ans = 1e9;
for (int j=1;j<=n;j++) ans = min(ans, dp[(int)E.size()-1][j]);
printf("%d\n", ans);
return 0;
}
