#include <bits/stdc++.h>
using namespace std;
#define ar array
const int mxN=5e3;
int n, ans, d[mxN][mxN], nxt[mxN+1][10];
string s;
priority_queue<ar<int, 3>, vector<ar<int, 3>>, greater<ar<int, 3>>> pq;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> s;
fill(nxt[n], nxt[n]+10, n);
for(int i=n-1; ~i; --i) {
memcpy(nxt[i], nxt[i+1], 40);
nxt[i][s[i]-'a']=i;
}
int e=n-1;
while(e&&s[e-1]^'e')
--e;
memset(d, 0x3f, sizeof(d));
d[0][0]=0;
pq.push({0, 0, 0});
while(pq.size()) {
ar<int, 3> u=pq.top();
pq.pop();
if(u[0]>d[u[1]][u[2]])
continue;
if(u[1]>=e) {
ans=u[0];
break;
}
vector<ar<int, 3>> t;
for(int k=0; k<10; ++k)
if(k^4&&nxt[u[2]+1][k]<n)
t.push_back({2, u[1], nxt[u[2]+1][k]});
if(u[2])
t.push_back({1, u[1], u[2]-1});
if(nxt[u[1]+1][4]<u[2]) {
int y=n;
for(int j=0; j<10; ++j)
if(j^4)
y=min(y, nxt[nxt[u[1]+1][4]][j]);
t.push_back({u[2]-nxt[u[1]+1][4], u[2], y});
}
for(ar<int, 3> v : t) {
if(u[0]+v[0]<d[v[1]][v[2]]) {
d[v[1]][v[2]]=u[0]+v[0];
pq.push({u[0]+v[0], v[1], v[2]});
}
}
}
for(char c : s)
ans+=c=='e';
cout << ans;
}
