#include <iostream>
#include <string>
#include <cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<iomanip>
#define _USE_MATH_DEFINES
#include <math.h>
#include <functional>
#include<complex>
using namespace std;

#define rep(i,x) for(ll i=0;i<x;i++)
#define repn(i,x) for(ll i=1;i<=x;i++)

typedef long long ll;
const ll INF = 1e17;
const ll MOD = 1000000007;
const ll MAX = 4000001;
const double eps = 1E-18;

ll max(ll a, ll b) {
	if (a > b) { return a; }
	return b;
}

ll min(ll a, ll b) {
	if (a > b) { return b; }
	return a;
}

ll gcd(ll a, ll b) {
	if (b == 0) { return a; }
	if (a < b) { return gcd(b, a); }
	return gcd(b, a % b);
}

ll lcm(ll a, ll b) {
	return a / gcd(a, b) * b;
}

struct edge {
	ll ind;
	ll fr;
	ll to;
	ll d;
};

class mint {
	long long x;
public:
	mint(long long x = 0) : x((x% MOD + MOD) % MOD) {}
	mint operator-() const {
		return mint(-x);
	}
	mint& operator+=(const mint& a) {
		if ((x += a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator-=(const mint& a) {
		if ((x += MOD - a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator*=(const  mint& a) {
		(x *= a.x) %= MOD;
		return *this;
	}
	mint operator+(const mint& a) const {
		mint res(*this);
		return res += a;
	}
	mint operator-(const mint& a) const {
		mint res(*this);
		return res -= a;
	}
	mint operator*(const mint& a) const {
		mint res(*this);
		return res *= a;
	}

	mint operator^(const ll& t)const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}

	mint pow(ll t) const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}
	// for prime MOD
	mint inv() const {
		return pow(MOD - 2);
	}
	mint& operator/=(const mint& a) {
		return (*this) *= a.inv();
	}
	mint operator/(const mint& a) const {
		mint res(*this);
		return res /= a;
	}

	friend ostream& operator<<(ostream& os, const mint& m) {
		os << m.x;
		return os;
	}
};

///////////////////////////

template<typename T>
struct BIT {
	ll n;
	vector<T> bt;
	ll sz;

	BIT(ll n0) {
		n = n0;
		sz = 1;
		while (sz < n) { sz *= 2; }
		bt.assign(sz + 1, 0);
	}

	ll sum(ll i) {
		T ret = 0;
		for (ll x = i; x > 0; x -= x & (-x)) {
			ret += bt[x];
		}
		return ret;
	}

	void add(ll i, ll w) {
		for (ll x = i; x <= sz; x += x & (-x)) {
			bt[x] += w;
		}
		return;
	}
};


int main() {
	
	ll N;
	cin >> N;

	vector<ll> W(N + 1), B(N + 1);
	repn(i, 2 * N) {
		char c;
		ll a;
		cin >> c >> a;

		if (c == 'W') { W[a] = i; }
		else { B[a] = i; }
	}

	vector<vector<ll>> x(N + 1, vector<ll>(N + 1,0));
	vector<vector<ll>> y(N + 1, vector<ll>(N + 1,0));

	rep(i, N+1) {
		BIT<ll> s(2 * N);

		repn(k, i) {
			ll t = W[k];
			s.add(t, 1);
		}

		repn(j, N) {
			ll t = B[j];
			x[i][j] = s.sum(t);
			s.add(t, 1);
		}
	}

	rep(j, N + 1) {
		BIT<ll> s(2 * N);

		repn(k, j) {
			ll t = B[k];
			s.add(t, 1);
		}

		repn(i, N) {
			ll t = W[i];
			y[i][j] = s.sum(t);
			s.add(t, 1);
		}
	}

	vector<vector<ll>> dp(N + 1, vector<ll>(N + 1, 0));
	rep(i, N+1)rep(j, N+1) {
		if (i > 0) { dp[i][j] = max(dp[i][j], dp[i - 1][j] + y[i][j]); }
		if (j > 0) { dp[i][j] = max(dp[i][j], dp[i][j - 1] + x[i][j]); }
	}

	ll ans = N * (2 * N - 1) - dp[N][N];
	cout << ans << endl;


	system("PAUSE");
}


Measured memory_bytes: 94584