#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(a, b) for(int a = 0; a < (b); ++a)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(), a.end()
const int LIM=7e4+7, INF=1e9+7;
vector<pair<int,int>>V[LIM];
int nxt[LIM][10], odl[LIM][10], odl2[LIM], kiedy[10];
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int n, ans=INF, x=0;
string s;
cin >> n >> s;
rep(i, n) {
if(s[i]=='e') {
s[i]='a';
x=i;
} else if(s[i]=='a') s[i]='e';
}
rep(i, 10) kiedy[i]=INF;
for(int i=n-1; i>=0; --i) {
rep(j, 10) {
nxt[i][j]=kiedy[j];
odl[i][j]=INF;
if(j && kiedy[j]<INF) V[kiedy[j]].pb({i, 2});
}
odl2[i]=INF;
kiedy[s[i]-'a']=i;
}
rep(i, n-1) V[i].pb({i+1, 1});
priority_queue<pair<int,pair<int,int>>>q;
q.push({0, {x, 0}});
while(!q.empty()) {
int o=-q.top().st, p=q.top().nd.st; q.pop();
if(odl2[p]<=o) continue;
odl2[p]=o;
for(auto i : V[p]) if(odl2[i.st]>o+i.nd) {
q.push({-o-i.nd, {i.st, 0}});
}
}
q.push({0, {0, 0}});
while(!q.empty()) {
int o=-q.top().st, a=q.top().nd.st, b=q.top().nd.nd; q.pop();
if(o>=odl[a][b]) continue;
odl[a][b]=o;
int p=nxt[a][b];
if(!b) p=a;
if(nxt[p][0]==INF) {
ans=min(ans, o);
} else {
ans=min(ans, o+odl2[a]+x-nxt[p][0]);
}
for(int i=1; i<10; ++i) if(nxt[a][i]<INF && nxt[a][i]>=p) {
if(nxt[p][0]>nxt[a][i]) {
if(odl[nxt[a][i]][i]==INF) q.push({-o-2, {nxt[a][i], 0}});
} else {
int mi=INF, c=i;
for(int j=1; j<10; ++j) mi=min(mi, nxt[nxt[p][0]][j]);
if(nxt[a][i]==mi) c=0;
if(odl[mi][c]==INF) q.push({-o-2-nxt[a][i]+nxt[p][0], {mi, c}});
}
}
}
rep(i, n) if(s[i]=='a') ++ans;
cout << ans << '\n';
}
