#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int MAX=200005;
int N=4;
char A[MAX]="soolnlsn";
map<char,vector<int>> idxs;
vector<int> L;
vector<int> R;
int pos[MAX];
bool lr[MAX];
int mv[MAX][2];
int D[MAX];
int main(){
cin>>N; cin>>A;
for (int i=0;i<2*N;i++){
idxs[A[i]].push_back(i);
}
for (auto pr:idxs){
char c=pr.first;
int l=idxs[c].size();
for (int i=0;i<l/2;i++){
L.push_back(idxs[c][i]);
R.push_back(idxs[c][l-1-i]);
}
}
for (int i=0;i<L.size();i++){
pos[L[i]]=i,pos[R[i]]=i;
lr[L[i]]=1;
lr[R[i]]=0;
D[i]=(R[i]-L[i])-N;
}
for (int i=0;i<2*N;i++){
int x=pos[i];
int dist=D[x];
if (dist<0 && !lr[i]){
dist=-dist;
for (int j=i;j<i+dist;j++){
lr[j] = lr[j+1];
pos[j] = pos[j+1];
mv[pos[j]][lr[j]]-=1;
lr[j] ? D[pos[j]]++ : D[pos[j]]--;
}
lr[i+dist]=0;
pos[i+dist]=x;
mv[x][0]+=dist;
D[x]+=dist;
}else if (dist>0 && lr[i]){
for (int j=i;j<i+dist;j++){
lr[j] = lr[j+1];
pos[j] = pos[j+1];
mv[pos[j]][lr[j]]-=1;
lr[j] ? D[pos[j]]++ : D[pos[j]]--;
}
lr[i+dist]=1;
pos[i+dist]=x;
mv[x][1]+=dist;
D[x]-=dist;
}
}
ll ans=0;
for (int i=0;i<N;i++){
ans+=abs(mv[i][0]);
ans+=abs(mv[i][1]);
//cout<<L[i]<<' '<<R[i]<<'\n';
//cout<<mv[i][0]<<' '<<mv[i][1]<<'\n';
}
cout<<ans/2;
}
