#include <cassert>// c
#include <iostream>// io
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>// container
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <algorithm>// other
#include <complex>
#include <numeric>
#include <functional>
#include <random>
#include <regex>
using namespace std;

typedef long long ll;typedef unsigned long long ull;typedef long double ld;

#define ALL(c) c.begin(),c.end()
#define IN(l,v,r) (l<=v && v < r)
template<class T> void UNIQUE(T& v){v.erase(unique(ALL(v)),v.end());}
//debug==
#define DUMP(x) cerr << #x <<" = " << (x)
#define LINE() cerr<< " (L" << __LINE__ << ")"

struct range{
	struct Iter{
		int v,step;
		Iter& operator++(){v+=step;return *this;}
		bool operator!=(Iter& itr){return v<itr.v;}
		int& operator*(){return v;}
	};
	Iter i, n;
	range(int i, int n,int step):i({i,step}), n({n,step}){}
	range(int i, int n):range(i,n,1){}
	range(int n):range(0,n){}
	Iter& begin(){return i;}
	Iter& end(){return n;}
};
struct rrange{
	struct Iter{
		int v,step;
		Iter& operator++(){v-=step;return *this;}
		bool operator!=(Iter& itr){return v>itr.v;}
		int& operator*(){return v;}
	};
	Iter i, n;
	rrange(int i, int n,int step):i({i-1,step}), n({n-1,step}){}
	rrange(int i, int n):rrange(i,n,1){}
	rrange(int n) :rrange(0,n){}
	Iter& begin(){return n;}
	Iter& end(){return i;}
};

//input
template<typename T1,typename T2> istream& operator >> (istream& is,pair<T1,T2>& p){return is>>p.first>>p.second;}
template<typename T1> istream& operator >> (istream& is,tuple<T1>& t){return is >> get<0>(t);}
template<typename T1,typename T2> istream& operator >> (istream& is,tuple<T1,T2>& t){return is >> get<0>(t) >> get<1>(t);}
template<typename T1,typename T2,typename T3> istream& operator >> (istream& is,tuple<T1,T2,T3>& t){return is >>get<0>(t)>>get<1>(t)>>get<2>(t);}
template<typename T1,typename T2,typename T3,typename T4> istream& operator >> (istream& is,tuple<T1,T2,T3,T4>& t){return is >> get<0>(t)>>get<1>(t)>>get<2>(t)>>get<3>(t);}
template<typename T> istream& operator >> (istream& is,vector<T>& as){for(int i:range(as.size()))is >>as[i];return is;}
//output
template<typename T> ostream& operator << (ostream& os, const set<T>& ss){for(auto a:ss){if(a!=ss.begin())os<<" "; os<<a;}return os;}
template<typename T1,typename T2> ostream& operator << (ostream& os, const pair<T1,T2>& p){return os<<p.first<<" "<<p.second;}
template<typename K,typename V> ostream& operator << (ostream& os, const map<K,V>& m){bool isF=true;for(auto& p:m){if(!isF)os<<endl;os<<p;isF=false;}return os;}
template<typename T1> ostream& operator << (ostream& os, const tuple<T1>& t){return os << get<0>(t);}
template<typename T1,typename T2> ostream& operator << (ostream& os, const tuple<T1,T2>& t){return os << get<0>(t)<<" "<<get<1>(t);}
template<typename T1,typename T2,typename T3> ostream& operator << (ostream& os, const tuple<T1,T2,T3>& t){return os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t);}
template<typename T1,typename T2,typename T3,typename T4> ostream& operator << (ostream& os, const tuple<T1,T2,T3,T4>& t){return os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t)<<" "<<get<3>(t);}
template<typename T> ostream& operator << (ostream& os, const vector<T>& as){for(int i:range(as.size())){if(i!=0)os<<" "; os<<as[i];}return os;}
template<typename T> ostream& operator << (ostream& os, const vector<vector<T>>& as){for(int i:range(as.size())){if(i!=0)os<<endl; os<<as[i];}return os;}

// values
template<typename T> inline T INF(){assert(false);};
template<> inline int INF<int>(){return 1<<28;};
template<> inline ll INF<ll>(){return 1LL<<60;};
template<> inline double INF<double>(){return 1e16;};
template<> inline long double INF<long double>(){return 1e16;};

template<class T> inline T EPS(){assert(false);};
template<> inline int EPS<int>(){return 1;};
template<> inline ll EPS<ll>(){return 1LL;};
template<> inline double EPS<double>(){return 1e-12;};
template<> inline long double EPS<long double>(){return 1e-12;};

// min{2^r | n < 2^r}
template<typename T> inline T upper_pow2(T n){ T res=1;while(res<n)res<<=1;return res;}
// max{d | 2^d  <= n}
template<typename T> inline T msb(T n){ int d=62;while((1LL<<d)>n)d--;return d;}

template<typename T,typename U> T pmod(T v,U M){return (v%M+M)%M;}


template<typename T> class Monoid{
public:
	virtual T e()=0,c(T,T)=0;
};

template<typename T> class MaxMonoid:public Monoid<T>{
public:
	T e(){return -INF<T>();}
	T c(T a,T b){return max(a,b);}
	static MaxMonoid<T>& i(){static MaxMonoid<T> i;return i;}
};

template<class T> class SparseTable{
public:
	vector<vector<T>> dbl;Monoid<T>& m;
	SparseTable(const vector<T>& as,Monoid<T>& m):dbl(msb(as.size())+1,vector<T>(as.size())),m(m){
		copy(ALL(as),dbl[0].begin());
		for(int l:range(1,dbl.size()))
			for(int i:range(dbl[l].size()))
				dbl[l][i]=m.c(dbl[l-1][i],dbl[l-1][i+(1<<(l-1))]);
	}
	inline T get(int v){return dbl[0][v];}
	T query(int a,int b){ //[a,b)
		if(a > b) assert(false);
		if(a == b) return m.e();
		int l=msb(b-a);
		return m.c(dbl[l][a],dbl[l][b-(1<<l)]);
	}
};

template <typename T,typename Func> T satisfy_mini(Func P,T l ,T r){//(l |sep| r)
	l -= EPS<T>();
	while(r-l>EPS<T>()){
		T m=(l+r)/2;
		(P(m)?r:l)=m;
	}
	return r;
}

template<typename T> struct Fenwick{
// public:
	int size;
	vector<T> dat;

	inline T e(){ return 0;}
	inline T c(T x,T y){return x+y;}
	inline T inv(T x){return -x;}
	Fenwick(int n):size(n){
		dat = vector<T>(n+1);
	}
	Fenwick():size(0){
		dat = vector<T>(1);

	}
	T query(int n){// [0,n)
		T s= e();
		while(n>0){
			s = c(s,dat[n]);
			n -= n&-n;//low
		}
		return s;
	}
	void add(int i,T x){//[0,...i...,n)
		i++;
		while(i<=size){
			dat[i] = c(dat[i],x);
			i += i&-i;//next
		}
	}
	T query(int a,int b){// [a,b)
		return c(query(b),inv(query(a)));
	}

	T lower_bound(T a){//minarg [0,n) <= a
		T sum = 0;
		int i = 0, b = msb(size + 1);
		while(b >= 0){
			if(i + (1 << b) < size + 1 && sum + dat[i + (1 << b)] < a){
				sum += dat[i + (1 << b)];
				i += 1 << b;
			}
			b--;
		}
		return i + 1;
	}
};


class Main{
	public:

	void run(){
		int N;cin >> N;
		vector<char> cs(2*N);
		vector<int> nums(2*N);
		vector<vector<int>> pos(2,vector<int>(N));
		for(int i:range(2*N)){
			cin >> cs[i] >> nums[i];nums[i]--;
			pos[cs[i]=='B'][nums[i]] = i;
		}

		// cerr << pos << endl;

		vector<vector<ll>> dp(N+1,vector<ll>(N+1,INF<ll>()));
		dp[0][0] = 0;

		Fenwick<int> fen(2*N);
		for(int bc:range(N+1)){
			if(IN(0,bc-1,N)) fen.add(pos[1][bc-1],1);
			for(int wc:range(N+1)){
				if(IN(0,wc-1,N)) fen.add(pos[0][wc-1],1);
				if(bc < N){
					dp[bc+1][wc] = min(dp[bc+1][wc], dp[bc][wc] + pos[1][bc] - fen.query(0,pos[1][bc]));
				}
				if(wc < N){
					dp[bc][wc+1] = min(dp[bc][wc+1], dp[bc][wc] + pos[0][wc] - fen.query(0,pos[0][wc]));
				}
			}
			for(int wc:range(N)) fen.add(pos[0][wc],-1);
		}

		cout << dp[N][N] << endl;
	}
};

int main(){
	cout <<fixed<<setprecision(20);
	cin.tie(0);
	ios::sync_with_stdio(false);
	Main().run();
	return 0;
}


Measured memory_bytes: 31616