#include <iostream>
#include <queue>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <stack>
#include <limits>
#include <climits>
#include <cassert>
#include <fstream>
#include <cstring>
#include <cmath>
#include <bitset>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdio>
#include <ciso646>
#include <set>
#include <array>
#include <unordered_map>
#include <unordered_set>
#include <type_traits>

using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

#define inf 0x3f3f3f3f3f3f3f3f
#define PB push_back
#define MP make_pair
#define ALL(a) (a).begin(),(a).end()
#define SET(a,c) memset(a,c,sizeof a)
#define CLR(a) memset(a,0,sizeof a)
#define VS vector<string>
#define VI vector<ll>
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define MIN(a,b) (a>b?b:a)
#define MAX(a,b) (a>b?a:b)
#define pi 2*acos(0.0)
#define INFILE() freopen("in0.txt","r",stdin)
#define OUTFILE()freopen("out0.txt","w",stdout)
#define ll long long
#define ull unsigned long long
#define pii pair<ll,ll>
#define pcc pair<char,char>
#define pic pair<ll,char>
#define pci pair<char,ll>
#define eps 1e-14
#define FST first
#define SEC second
#define SETUP cin.tie(0), ios::sync_with_stdio(false), cout << setprecision(15) << std::fixed;

namespace {
	struct input_returnner {
		ll N; input_returnner(ll N_ = 0) :N(N_) {}
		template<typename T> operator vector<T>() const { vector<T> res(N); for (auto &a : res) cin >> a; return std::move(res); }
		template<typename T> operator T() const { T res; cin >> res; return res; }
		template<typename T> T operator - (T right) { return T(input_returnner()) - right; }
		template<typename T> T operator + (T right) { return T(input_returnner()) + right; }
		template<typename T> T operator * (T right) { return T(input_returnner()) * right; }
		template<typename T> T operator / (T right) { return T(input_returnner()) / right; }
		template<typename T> T operator << (T right) { return T(input_returnner()) << right; }
		template<typename T> T operator >> (T right) { return T(input_returnner()) >> right; }
	};
	template<typename T> input_returnner in() { return in<T>(); }
	input_returnner in() { return input_returnner(); }
	input_returnner in(ll N) { return std::move(input_returnner(N)); }
}

template < typename T >
struct is_vector : std::false_type {};

template < typename T >
struct is_vector<std::vector<T>> : std::true_type {};

template < typename T >
constexpr bool is_vector_v = is_vector<T>::value;

template <typename T>
std::ostream& operator<< (std::ostream& out, const std::vector<T>& v) {
	if (!v.empty()) {
		for (int i = 0; i < v.size(); ++i) {
			out << v[i] << (i == v.size() - 1 ? "\n" : (is_vector_v<T> ? "" : ", "));
		}
	}
	return out;
}

ll MOD = 1e9 + 7;

class prime ;

void solve();

signed main() {
	SETUP;
	solve();
#ifdef _DEBUG
	system("pause");
#endif
	return 0;
}

#define int ll

void solve() {
	int N; cin >> N;
	vector<pair<bool, int> > field; // isWhite, number
	map<pair<bool, int>, int> pos;

	for (int i = 0; i < 2 * N; ++i) {
		char c; int a; cin >> c >> a;
		field.emplace_back(c == 'W', a);
		pos[make_pair(c == 'W', a)] = i;
	}

	vector<vector<int> > blackCnt(N + 1, vector<int>(field.size()+2));
	vector<vector<int> > whiteCnt(N + 1, vector<int>(field.size()+2));


	for (int i = 1; i < N + 1; ++i) {
		blackCnt[i][field.size()-1] = (not field[field.size()-1].first and field[field.size()-1].second <= i ? 1 : 0);
		whiteCnt[i][field.size()-1] = (field[field.size()-1].first and field[field.size()-1].second <= i ? 1 : 0);
		for (int j = field.size()-2; j >= 0; --j) {
			blackCnt[i][j] = blackCnt[i][j + 1];
			whiteCnt[i][j] = whiteCnt[i][j + 1];
			if (not field[j].first and field[j].second <= i) blackCnt[i][j]++;
			if (field[j].first and field[j].second <= i) whiteCnt[i][j]++;
		}
	}
	

	vector<vector<int> > dp(N+1, vector<int>(N+1, inf));
	dp[0][0] = 0;
	for (int i = 1; i < N+1; ++i) {
		int p = pos[make_pair(false, i)];
		dp[0][i] = dp[0][i - 1] + blackCnt[i - 1][p+1];
	}
	for (int i = 1; i < N+1; ++i) {
		int p = pos[make_pair(true, i)];
		dp[i][0] = dp[i-1][0] + whiteCnt[i - 1][p+1];
	}

	for (int w = 1; w <= N; ++w) {
		for (int b = 1; b <= N; ++b) {
			int blackPos = pos[make_pair(false, b)];
			int whitePos = pos[make_pair(true, w)];
			dp[w][b] = min(dp[w - 1][b] + blackCnt[b][whitePos + 1] + whiteCnt[w - 1][whitePos + 1], dp[w][b - 1] + blackCnt[b - 1][blackPos + 1] + whiteCnt[w][blackPos + 1]);
		}
	}
	cout << dp[N][N] << endl;
}



Measured memory_bytes: 157184