#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> P;
typedef pair<int,int> Pi;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define FOR(i, a, b) for (ll i = a; i < b; i++)
#define fi first
#define se second
#define endl "\n"

template<typename T> inline bool chmax(T &a, T b){if(a<b){a=b;return true;}return false;}
template<typename T> inline bool chmin(T &a, T b){if(a>b){a=b;return true;}return false;}
template<typename T> ostream& operator<<(ostream& s,const complex<T>& d) {return s<<"("<<d.real()<<", "<<d.imag()<< ")";}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const pair<T1,T2>& d) {return s<<"("<<d.first<<", "<<d.second<<")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& d){
	int len=d.size();
	rep(i,len){
		s<<d[i];if(i<len-1) s<<" ";
	}
	return s;
}
template<typename T> ostream& operator<<(ostream& s,const vector<vector<T>>& d){
	int len=d.size();
	rep(i,len){
		s<<d[i]<<endl;
	}
	return s;
}
template<typename T> ostream& operator<<(ostream& s,const set<T>& v){
	s<<"{ ";
	for(auto itr=v.begin();itr!=v.end();++itr) {
		if (itr!=v.begin()) {s<< ", ";}
		s<<(*itr);
	}
	s<<" }";
	return s;
}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const map<T1,T2>& m){
	s<<"{"<<endl;
	for(auto itr=m.begin();itr!=m.end();++itr){
		s<<" "<<(*itr).first<<" : "<<(*itr).second<<endl;
	}
	s<<"}"<<endl;
	return s;
}

const ll mod=1e9+7;
const ll inf=1e17;
const int INF=1e9;
const double PI=acos(-1);
const double EPS=1e-10;

template<typename Monoid,typename F>
struct SegmentTree{
	int sz;
	vector<Monoid> node;
	const F op;//演算
	const Monoid e;//単位元
	SegmentTree(int n,const F op,const Monoid &e):op(op),e(e){
		sz=1;
		while(sz<n) sz*=2;
		node.assign(2*sz,e);
	}
	void build(const vector<Monoid> &v){
		int n=v.size();
		for(int i=0;i<n;i++) node[i+sz-1]=v[i];
		for(int i=sz-2;i>=0;i--) node[i]=op(node[2*i+1],node[2*i+2]);
	}
	void update(int k,const Monoid &x){
		k+=sz-1;
		node[k]=x;
		while(k>0){
			k=(k-1)/2;
			node[k]=op(node[2*k+1],node[2*k+2]);
		}
	}
	Monoid query(int a,int b,int k=0,int l=0,int r=-1){
		if(r<0) r=sz;
		if(r<=a || b<=l) return e;
		if(a<=l && r<=b) return node[k];
		else{
			Monoid vl=query(a,b,2*k+1,l,(l+r)/2);
			Monoid vr=query(a,b,2*k+2,(l+r)/2,r);
			return op(vl,vr);
		}
	}
	Monoid operator[](const int &k)const{
		return node[k+sz-1];
	}
};

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n;
	cin>>n;
	vector<char> c(2*n);
	vector<int> a(2*n);
	auto f=[](int a,int b){return a+b;};
	SegmentTree<int,decltype(f)> seg1(n,f,0),seg2(n,f,0);
	vector<vector<int>> w(n+1,vector<int>(n+1,0)),b(n+1,vector<int>(n+1,0)),dp(n+1,vector<int>(n+1,INF));
	rep(i,2*n){
		cin>>c[i]>>a[i];
		a[i]--;
	}
	rep(i,2*n){
		if(c[i]=='W'){
			rep(j,n+1){
				w[a[i]][j]=seg1.query(a[i]+1,n)+seg2.query(j,n);
			}
			seg1.update(a[i],1);
		}else{
			rep(j,n+1){
				b[j][a[i]]=seg1.query(j,n)+seg2.query(a[i]+1,n);
			}
			seg2.update(a[i],1);
		}
	}
	dp[0][0]=0;
	rep(i,n+1)rep(j,n+1){
		if(i!=n) chmin(dp[i+1][j],dp[i][j]+w[i][j]);
		if(j!=n) chmin(dp[i][j+1],dp[i][j]+b[i][j]);
	}
	cout<<dp[n][n]<<endl;
}

Measured memory_bytes: 49536