#include <iostream>
#include <algorithm>
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <array>
#include <unordered_map>
#include <complex>
#include <deque>
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>
using namespace std;

#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define bit(n) (1LL<<(n))
#define sz(x) ((int)(x).size())
#define TEN(n) ((ll)(1e##n))
#define fst first
#define snd second

string DBG_DLM(int &i){return(i++==0?"":", ");}
#define DBG_B(exp){int i=0;os<<"{";{exp;}os<<"}";return os;}
template<class T>ostream&operator<<(ostream&os,vector<T>v);
template<class T>ostream&operator<<(ostream&os,set<T>v);
template<class T>ostream&operator<<(ostream&os,queue<T>q);
template<class T>ostream&operator<<(ostream&os,priority_queue<T>q);
template<class T,class K>ostream&operator<<(ostream&os,pair<T,K>p);
template<class T,class K>ostream&operator<<(ostream&os,map<T,K>mp);
template<class T,class K>ostream&operator<<(ostream&os,unordered_map<T,K>mp);
template<int I,class TPL>void DBG(ostream&os,TPL t){}
template<int I,class TPL,class H,class...Ts>void DBG(ostream&os,TPL t){os<<(I==0?"":", ")<<get<I>(t);DBG<I+1,TPL,Ts...>(os,t);}
template<class T,class K>void DBG(ostream&os,pair<T,K>p,string delim){os<<"("<<p.first<<delim<<p.second<<")";}
template<class...Ts>ostream&operator<<(ostream&os,tuple<Ts...>t){os<<"(";DBG<0,tuple<Ts...>,Ts...>(os,t);os<<")";return os;}
template<class T,class K>ostream&operator<<(ostream&os,pair<T,K>p){DBG(os,p,", ");return os;}
template<class T>ostream&operator<<(ostream&os,vector<T>v){DBG_B(forr(t,v){os<<DBG_DLM(i)<<t;});}
template<class T>ostream&operator<<(ostream&os,set<T>s){DBG_B(forr(t,s){os<<DBG_DLM(i)<<t;});}
template<class T>ostream&operator<<(ostream&os,queue<T>q){DBG_B(for(;q.size();q.pop()){os<<DBG_DLM(i)<<q.front();});}
template<class T>ostream&operator<<(ostream&os,priority_queue<T>q){DBG_B(for(;q.size();q.pop()){os<<DBG_DLM(i)<<q.top();});}
template<class T,class K>ostream&operator<<(ostream&os,map<T,K>m){DBG_B(forr(p,m){os<<DBG_DLM(i);DBG(os,p,"->");});}
template<class T,class K>ostream&operator<<(ostream&os,unordered_map<T,K>m){DBG_B(forr(p,m){os<<DBG_DLM(i);DBG(os,p,"->");});}
#define DBG_OVERLOAD(_1,_2,_3,_4,_5,_6,macro_name,...)macro_name
#define DBG_LINE(){char s[99];sprintf(s,"line:%3d | ",__LINE__);cerr<<s;}
#define DBG_OUTPUT(v){cerr<<(#v)<<"="<<(v);}
#define DBG1(v,...){DBG_OUTPUT(v);}
#define DBG2(v,...){DBG_OUTPUT(v);cerr<<", ";DBG1(__VA_ARGS__);}
#define DBG3(v,...){DBG_OUTPUT(v);cerr<<", ";DBG2(__VA_ARGS__);}
#define DBG4(v,...){DBG_OUTPUT(v);cerr<<", ";DBG3(__VA_ARGS__);}
#define DBG5(v,...){DBG_OUTPUT(v);cerr<<", ";DBG4(__VA_ARGS__);}
#define DBG6(v,...){DBG_OUTPUT(v);cerr<<", ";DBG5(__VA_ARGS__);}
#define DEBUG0(){DBG_LINE();cerr<<endl;}
#ifdef LOCAL
#define out(...){DBG_LINE();DBG_OVERLOAD(__VA_ARGS__,DBG6,DBG5,DBG4,DBG3,DBG2,DBG1)(__VA_ARGS__);cerr<<endl;}
#else
#define out(...)
#endif

using ll=long long;
using pii=pair<int,int>;using pll=pair<ll,ll>;using pil=pair<int,ll>;using pli=pair<ll,int>;
using vs=vector<string>;using vvs=vector<vs>;using vvvs=vector<vvs>;
using vb=vector<bool>;using vvb=vector<vb>;using vvvb=vector<vvb>;
using vi=vector<int>;using vvi=vector<vi>;using vvvi=vector<vvi>;
using vl=vector<ll>;using vvl=vector<vl>;using vvvl=vector<vvl>;
using vd=vector<double>;using vvd=vector<vd>;using vvvd=vector<vvd>;
using vpii=vector<pii>;using vvpii=vector<vpii>;using vvvpii=vector<vvpii>;
template<class A,class B>bool amax(A&a,const B&b){return b>a?a=b,1:0;}
template<class A,class B>bool amin(A&a,const B&b){return b<a?a=b,1:0;}
ll ri(){ll l;cin>>l;return l;} string rs(){string s;cin>>s;return s;}

template <typename T> struct BinaryIndexedTree0 {
	const int N;
	vector<T> val;

	BinaryIndexedTree0(int N) : N(N), val(N) {}

	T sum(int i) const {
		T s = 0;
		--i;
		if (i >= N) i = N - 1;
		for (; i >= 0; i = (i & (i + 1)) - 1) s += val[i];
		return s;
	}

	T sum(int l, int r) const {
		return sum(r) - sum(l);
	}

	void add(int i, T x) {
		for (; i < N; i |= i + 1) val[i] += x;
	}

	void set(int i, T x) {
		T c = sum(i, i + 1);
		add(i, x - c);
	}

	int lower_bound(T w) const {
		int x = 0;

		for (int k = (1 << (31 - __builtin_clz(N))) - 1; ; k >>= 1) {
			if (x + k < N && val[x + k] < w) {
				w -= val[x + k];
				x += k + 1;
			}
			if (k == 0) break;
		}
		return x;
	}
};
template<class V> ostream& operator<<(ostream& os, const BinaryIndexedTree0<V>& ft) {
	vector<V> vec;
	for (int i = 0; i < ft.N; i++) {
		vec.emplace_back(ft.sum(i, i+1));
	}
	os << vec;
	return os;
}


/*

B 1
W 2
B 3
W 1
W 3
B 2

B 1
W 1
W 2
B 2
B 3
W 3

B 1
W 1
W 2
W 3
B 2
B 3

B 4
W 4
B 3
W 3
B 2
W 2
B 1
W 1

B 1
B 2
B 4
W 4
B 3
W 3
W 2
W 1



B 1
B 2
B 3
B 4
W 1
W 2
W 3
W 4

同じ色同士のswapは絶対必要。(転倒数)
違う色のswapを最小化。

*/
const int inf = 1e9;

template <class T> vector<int> compress(const vector<T> &orig) {
	vector<int> ret(orig.size());
	vector<T> a(orig);
	sort(a.begin(), a.end()); a.erase(unique(a.begin(), a.end()), a.end());
	for (size_t i = 0; i < orig.size(); i++) {
		ret[i] = distance(a.begin(), lower_bound(a.begin(), a.end(), orig[i]));
	}
	return ret;
}

ll countInv(vi A) {
	int n = sz(A);
	A = compress(A);
	BinaryIndexedTree0<int> ft(n);
	ll ret = 0;
	rep(i, n) {
		ret += ft.sum(A[i], n);
		ft.add(A[i], 1);
	}
	return ret;
}

ll solve() {
	int n = ri();

	string C;
	vi B(n), W(n);
	rep(i, n * 2) {
		char c = rs()[0];
		int x = ri()-1;
		if (c == 'B') B[x] = i;
		else W[x] = i;
		C += c;
	}

	ll invW = countInv(W), invB = countInv(B);
	out(invW, invB);

	vi RB(2*n+1), RW(2*n+1);
	rep(i, 2*n) {
		RB[i+1] = RB[i];
		RW[i+1] = RW[i];
		if (C[i] == 'B') {
			RB[i+1]++;
		}
		else {
			RW[i+1]++;
		}
	}
	out(C, RB, RW);
	out(B, W);

	vvi dp(n+1, vi(n+1, inf));
	dp[0][0] = 0;

	BinaryIndexedTree0<int> ftB(n*2+2);
	rep(i, n) {
		BinaryIndexedTree0<int> ftW(n*2+2);
		rep(j, n) {
			out(i,j,dp[i][j], ftB, ftW);
			{
				int pos = B[i];
				int nuku = RW[pos+1] - ftW.sum(pos+1);
				amin(dp[i+1][j], dp[i][j] + nuku);
				out(i,j,pos,nuku, dp[i+1][j]);
			}
			{
				int pos = W[j];
				int nuku = RB[pos+1] - ftB.sum(pos+1);
				amin(dp[i][j+1], dp[i][j] + nuku);
				out(i,j,pos,nuku, dp[i][j+1]);
			}
			out(i,j,dp[i][j], dp[i+1][j], dp[i][j+1]);
			ftW.add(W[j], 1);
		}
		ftB.add(B[i], 1);
	}

	out(dp);

	ll ans = inf;
	rep(i, n) {
		amin(ans, dp[i][n]);
		amin(ans, dp[n][i]);
	}
	out(ans);

	return ans + invW + invB;

}

void Main() {
	cout << solve() << endl;
}
signed main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	Main();
	return 0;
}


Measured memory_bytes: 16128