#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 t;
cin >> n >> t;
vector<int> e;
string s;
for (char c : t) {
if (c != 'e') {
s += c;
e.push_back(0);
} else {
e.back()++;
}
}
n = s.size();
auto sum =[&](int l, int r) {
ll s = 0;
for (;l <= r; l++)
s += e[l];
return s;
};
vector memo(n, vector(n, -1));
auto dp = [&](auto& dp, int i, int ne)->int {
if (ne == n) return 0;
int& res = memo[i][ne];
if (res!=-1) return res;
res = inf;
set<char> seen;
for (int j = i+1; j < n; j++) {
if (seen.count(s[j])) continue;
seen.insert(s[j]);
int nne = j;
while (nne < n && e[nne] == 0) nne++;
int dist = j - ne;
int ec = sum(ne, j-1);
res = min(res, dp(dp, ne, nne) + max(0, dist) + max(0, ec * 2 - 1) + 2);
}
//cout << i << ' ' << ne << ' ' << res << '\n';
return res;
};
int ne = 0;
while (ne < n && e[ne] == 0) ne++;
cout << dp(dp, 0, ne) << '\n';
return 0;
}
