#include<bits/stdc++.h>
#pragma GCC optimize("unroll-loops,no-stack-protector,Ofast")
using namespace std;
typedef long long ll;
typedef pair<ll,ll> pll;
const ll N=7e4+5;
const ll INF=(1LL<<60);
#define REP(i,n) for(int i=0;i<n;i++)
#define REP1(i,n) for(int i=1;i<=n;i++)
#define X first
#define Y second
#define pb push_back
#define mp make_pair
#define lwb lower_bound
ll nxt[N][11],e[N];
unordered_map<ll,ll> dp[N];
string s;
vector<ll> loc;
ll n,m;
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);
cin>>n>>s;
REP(j,10)nxt[n][j]=n;
for(int i=n-1;i>=0;i--){
REP(j,10)nxt[i][j]=nxt[i+1][j];
nxt[i][s[i]-'a']=i;
e[i]=(s[i+1]=='e'?e[i+1]:i+1);
if(s[i]=='e')loc.pb(i);
}
reverse(loc.begin(),loc.end());
m=loc.size();
REP(i,n)dp[m][i]=0;
for(int i=m-1;i>=0;i--){
for(int j=n-1;j>=0;j--){
dp[i][j]=INF;
if(s[j]=='e')continue;
ll ii=lwb(loc.begin(),loc.end(),j)-loc.begin();
if(j>loc[i])dp[i][j]=min(dp[i][j],dp[ii][e[loc[i]]]+(j-loc[i]));
for(int k=0;k<10;k++){
if(k=='e'-'a'||nxt[j+1][k]==n)continue;
dp[i][j]=min(dp[i][j],dp[i][nxt[j+1][k]]+2);
}
}
}
cout<<dp[0][0]+m<<"\n";
//REP(i,m)REP(j,n)cout<<i<<" "<<j<<" "<<dp[i][j]<<"\n";
return 0;
}
