#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int inf = 1e9;
signed main() {
cin.tie(0)->sync_with_stdio(0);
int n;
string s;
cin >> n >> s;
vector memo(n, vector(n, -1));
auto dp = [&](auto& dp, int l, int ne)->int {
if (ne == n) return 0;
if (memo[l][ne] !=-1) return memo[l][ne];
vector seen(10, 0);
int res = inf;
int cnt = 0;
for (int r = l+1; r < n; r++) {
if (s[r] == 'e') {
if (r >= ne) cnt++;
continue;
}
if (seen[s[r] % 10]) continue;
seen[s[r] % 10] = 1;
if (cnt == 0) res = min(res, dp(dp, r, ne) + 2);
else {
int nne = r+1;
while (nne <n && s[nne] != 'e') nne++;
int cn = 0;
for (int i = ne; i < n; i++)
if (s[i] == 'e') cn++;
else break;
res = min(res, dp(dp, ne, nne) + 2 + (r - (ne + cn-1)) + cnt*2 - cn);
}
}
return memo[l][ne] = res;
};
int ne = find(s.begin(), s.end(), 'e') - s.begin();
cout << dp(dp, 0, ne)-1;
return 0;
}
