#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int MAX=100005;
int N=4;
char A[MAX]="soolnlsn";
map<char,vector<int>> idxs;
vector<int> L;
vector<int> R;
int pos[MAX];
int dist[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]);
}
}
ll ans=0;
for (int i=0;i<L.size();i++){
pos[L[i]]=i,pos[R[i]]=i;
dist[i]=abs((R[i]-L[i]) - (N));
ans+=dist[i];
}
cout<<ans/2;
}
