#include <iostream>
#include <fstream>
#include <cmath>  
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <numeric>
#include <functional>
#include <string> 
#include <vector>
#include <bitset>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>

using namespace std;
using ll = long long;

#define REP(i,n) for(long long i = 0; i < (n); i++)
#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define ALL(obj) (obj).begin(),(obj).end()

template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;

const ll MOD = (ll)1e9 + 7;
const ll HINF = (ll)1e18;
const ll LINF = (ll)1e9;
const long double PI = 3.1415926535897932384626433;

template <class T> void corner(bool flg, T hoge) { if (flg) { cout << hoge << endl; exit(0); } }
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) { o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o; }
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) { o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o; }
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) { o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o; }
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) { o << "{" << obj.first << ", " << obj.second << "}"; return o; }
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) { o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o; }
void print(void) { cout << endl; }
template <class Head> void print(Head&& head) { cout << head; print(); }
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) { cout << head << " "; print(forward<Tail>(tail)...); }
void YN(bool flg) { cout << ((flg) ? "YES" : "NO") << endl; }
void Yn(bool flg) { cout << ((flg) ? "Yes" : "No") << endl; }
void yn(bool flg) { cout << ((flg) ? "yes" : "no") << endl; }

//Binary Indexed Tree
class Binary_Indexed_Tree_Range_Sum_Query {
public:
	int N;
	vector<long long> node;

	Binary_Indexed_Tree_Range_Sum_Query(int N) : N(N), node(vector<long long>(N + 1, 0)) {
	}

	void update(int idx, long long var) {
		for (++idx; idx <= N; idx += idx & -idx) node[idx] += var;
	}

	long long getvar(int idx) {
		long long ret = 0;
		for (++idx; idx >= 1; idx -= idx & -idx) ret += node[idx];
		return ret;
	}
};


int main() {
	int N,M; cin >> N;
	M = 2 * N;


	V<ll> a(M);
	string S;
	REP(i,M){
		char c;
		cin >> c >> a[i];
		S.push_back(c);
	}

	V<V<ll>> costw(N+1,V<ll>(N+1,0)), costb(N + 1, V<ll>(N + 1, 0));
	Binary_Indexed_Tree_Range_Sum_Query BITw(N+1),BITb(N+1);

	REP(i,M){
		if (S[i] == 'W') {
			ll tmp = BITw.getvar(N) - BITw.getvar(a[i]);
			for (int j = 0; j <= N; ++j) {
				costw[a[i]][j] = tmp + BITb.getvar(N) - BITb.getvar(j);
			}
			BITw.update(a[i], 1);
		}
		if (S[i] == 'B') {
			ll tmp = BITb.getvar(N) - BITb.getvar(a[i]);
			for (int j = 0; j <= N; ++j) {
				costb[a[i]][j] = tmp + BITw.getvar(N) - BITw.getvar(j);
			}
			BITb.update(a[i], 1);
		}
	}
	V<V<ll>> dp(N + 1, V<ll>(N + 1, LINF));
	dp[0][0] = 0;
	dp[1][0] = costw[1][1];
	dp[0][1] = costb[1][1];
	
	for(int i = 0; i <= N; ++i){
		for(int j = 0; j <= N; ++j){
			if (i > 0 && j == 0) dp[i][j] = dp[i - 1][j] + costw[i][j];
			if (i == 0 && j > 0) dp[i][j] = dp[i][j - 1] + costb[j][i];
			if (i > 0 && j > 0) dp[i][j] = min(dp[i - 1][j] + costw[i][j], dp[i][j - 1] + costb[j][i]);
		}
	}
	cout << dp[N][N] << endl;


	return 0;
}

Measured memory_bytes: 94336