#define _USE_MATH_DEFINES
#include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <string>
#include <vector>
#include <utility>
#include <complex>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <deque>
#include <tuple>
#include <bitset>
#include <limits>
#include <algorithm>
#include <array>
#include <random>
#include <complex>
#include <regex>
using namespace std;
typedef long double ld;
typedef long long ll;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef complex<ld> compd;
#define quickIO()	{cin.tie(0);	cout.sync_with_stdio(false);}
#define reach(i,a)	for(auto i:a)
#define rep(i,n)	for(int i=0;i<((int)n);i++)
#define REP(i,n)	for(int i=0;i<=((int)n);i++)
#define srep(i,a,n)	for(int i=a;i<((int)n);i++)
#define SREP(i,a,n)	for(int i=a;i<=((int)n);i++)
#define rrep(i,n)	for(int i=n-1;i>=0;i--)
#define RREP(i,n)	for(int i=n;i>=0;i--)
#define all(a)	(a).begin(),(a).end()
#define mp(a,b)	make_pair(a,b)
#define mt	make_tuple
#define pb	push_back
template<typename T> istream& operator >> (istream& is, vector<T>& vec) {
	for (T& x : vec)	is >> x;
	return is;
}
template<typename T> ostream& operator << (ostream& os, vector<T>& vec) {
	os << "[";
	rep(i, vec.size())	os << (i ? ", " : "") << vec[i];
	os << "]";
	return os;
}
template<typename T> istream& operator >> (istream& is, pair<T, T>& p) {
	is >> p.first >> p.second;
	return is;
}
template<typename T> ostream& operator << (ostream& os, pair<T, T>& p) {
	os << "(" << p.first << ", " << p.second << ")";
	return os;
}
int bitcnt(ll x) {
	x = ((x & 0xAAAAAAAAAAAAAAAA) >> 1) + (x & 0x5555555555555555);
	x = ((x & 0xCCCCCCCCCCCCCCCC) >> 2) + (x & 0x3333333333333333);
	x = ((x & 0xF0F0F0F0F0F0F0F0) >> 4) + (x & 0x0F0F0F0F0F0F0F0F);
	x = ((x & 0xFF00FF00FF00FF00) >> 8) + (x & 0x00FF00FF00FF00FF);
	x = ((x & 0xFFFF0000FFFF0000) >> 16) + (x & 0x0000FFFF0000FFFF);
	x = ((x & 0xFFFFFFFF00000000) >> 32) + (x & 0x00000000FFFFFFFF);
	return x;
}
int bitcnt(int x) {
	x = ((x & 0xAAAAAAAA) >> 1) + (x & 0x55555555);
	x = ((x & 0xCCCCCCCC) >> 2) + (x & 0x33333333);
	x = ((x & 0xF0F0F0F0) >> 4) + (x & 0x0F0F0F0F);
	x = ((x & 0xFF00FF00) >> 8) + (x & 0x00FF00FF);
	x = ((x & 0xFFFF0000) >> 16) + (x & 0x0000FFFF);
	return x;
}
ll sqrtll(ll x) {
	ll left = 0, right = x;
	rep(i, 100) {
		ll mid = (left + right) >> 1;
		if (mid*mid <= x)	left = mid;
		else	right = mid;
	}
	return left;
}
ll gcd(ll a, ll b) {
	return b == 0 ? a : gcd(b, a%b);
}
#define debug(x)	printf("Case #%d: ", x)
#define DEBUG 0
const ll inf = 1e9;
const ld infl = 1e100;
const ll mod = 1e9 + 7;
const ld eps = 1e-9;
const int dx[] = { 1,0,-1,0,0 };
const int dy[] = { 0,1,0,-1,0 };

ll posW[4010];
ll posB[4010];
ll costW[4010][4010];
ll costB[4010][4010];
ll dp[4010][4010];

class BIT {
public:
	vll dat;
	int n;
	BIT(int _n) {
		n = 1;
		while (n <= _n)	n <<= 1;
		dat.assign(n + 1, 0);
	}

	void add(int k, ll v) {
		k++;
		while (k <= n) {
			dat[k] += v;
			k += -k & k;
		}
	}

	ll get(int k) {
		k++;
		ll ret = 0;
		while (k > 0) {
			ret += dat[k];
			k -= -k & k;
		}
		return ret;
	}
};

int main() {
	int n;	cin >> n;
	int m = 2 * n;
	vector<pii> dat;
	rep(i, m) {
		char c; int a;	cin >> c >> a;
		if (c == 'W') {
			dat.push_back(mp(0, a));
			posW[a] = i;
		}
		else {
			dat.push_back(mp(1, a));
			posB[a] = i;
		}
	}
	// number of bk
	REP(i, n) {
		BIT bit(m);
		rep(j, i) {
			bit.add(posB[j + 1], 1);
		}
		srep(j, i, m) {
			costW[j][i] = (posW[j - i + 1] - j) + (j - bit.get(posW[j - i + 1]));
			costB[j][i] = (posB[i + 1] - j) + (j - bit.get(posB[i + 1]));
			bit.add(posW[j - i + 1], 1);
		}
	}
	REP(i, m)	REP(j, n)	dp[i][j] = inf;
	dp[0][0] = 0;
	rep(i, m) {
		REP(j, min(i + 1, n)) {
			if (dp[i][j] == inf)	continue;
			dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + costW[i][j]);
			dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + costB[i][j]);
		}
	}
	cout << dp[m][n] << endl;
	return 0;
}

Measured memory_bytes: 376448