#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
// #define int long long
// #define double long double
#define rep(i,n) for (int i=0; i<(int)(n); ++i)
#define rep1(i,n) for (int i=1; i<(int)(n); ++i)
#define repeq(i,n) for (int i=0; i<=(int)(n); ++i)
#define rep1eq(i,n) for (int i=1; i<=(int)(n); ++i)
#define rrep(i,n) for (int i=(int)(n)-1; i>=0; --i)
#define rrep1(i,n) for (int i=(int)(n)-1; i>0; --i)
#define rrepeq(i,n) for (int i=(int)(n); i>=0; --i)
#define rrep1eq(i,n) for (int i=(int)(n); i>0; --i)
#define REP(i,a,b) for (int i=(int)(a); i<=(int)(b); ++i)
#define RREP(i,a,b) for (int i=(int)(a); i>=(int)(b); --i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using vb = vector<bool>;
template<typename T> using Graph = vector<vector<T>>;
template<typename T> using Spacial = vector<vector<vector<T>>>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int MOD = 1e9+7;
const int MOD2 = 998244353;
// const double EPS = 1e-9;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
string interval[2] = {" ", "\n"}; // {" ", "\n"}

template<typename T> struct is_plural : false_type{};
template<typename T1, typename T2> struct is_plural<pair<T1, T2>> : true_type{};
template<typename T> struct is_plural<vector<T>> : true_type{};
template<typename T> struct is_plural<complex<T>> : true_type{};
 
template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << " " << p.second; }
template<typename T> istream &operator>>(istream &is, vector<T> &vec) { for (auto itr = vec.begin(); itr != vec.end(); ++itr) is >> *itr; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec) { if (vec.empty()) return os; bool pl = is_plural<T>(); os << vec.front(); for (auto itr = ++vec.begin(); itr != vec.end(); ++itr) os << interval[pl] << *itr; return os; }
 
bool CoutYN(bool a, string y = "Yes", string n = "No") { cout << (a ? y : n) << "\n"; return a; }

template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

int modpow(int a, long long n, int mod = MOD) { int ret = 1; do { if (n & 1) ret = 1LL * ret * a % mod; a = 1LL * a * a % mod; } while (n >>= 1); return ret; }

template<typename T1, typename T2> bool CompareBySecond(pair<T1, T2> a, pair<T1, T2> b) { return a.second != b.second ? a.second < b.second : a.first < b.first; }
// counterclockwise from 12 o'clock direction
template<typename T> bool CompareBySlope(pair<T, T> a, pair<T, T> b) { if (a.first * b.first < 0) return a.first < b.first; if (a.first == 0) return a.second >= 0 || b.first > 0; if (b.first == 0) return b.second < 0 && a.first < 0; return a.second * b.first < a.first * b.second; }


/* -------- <templates end> -------- */


template<typename T>
struct BIT {
  vector<T> bit;
  const int sz;

  BIT(int n) : bit(n+1, 0), sz(n) {}

// [1, i] 1-indexed
  T sum(int i) {
    T s = 0;
    while (i > 0) { s += bit[i]; i -= i & -i; }
    return s;
  }

// [l, r] 1-indexed
  T sum(int l, int r) {
    return sum[r] - sum[l-1];
  }

  void add(int i, T x) {
    while (i <= sz) { bit[i] += x; i += i & -i; }
  }
};

void solve() {
  int n; cin >> n;
  Graph<int> g(2, vi(n+1));
  rep(i,2*n) {
    char c; int a; cin >> c >> a;
    g[c=='B'][a] = i;
  }

  Spacial<int> cost(2, Graph<int>(n+1, vi(n+1)));
  rep(c,2) {
    BIT<int> bit(2*n);
    rep1eq(i,n) {
      cost[c][i][0] = g[c][i] - bit.sum(g[c][i]);
      bit.add(g[c][i]+1, 1);
      rep1eq(j,n) {
        cost[c][i][j] = cost[c][i][j-1] - (g[1-c][j] < g[c][i]);
      }
    }
  }

  Graph<int> dp(n+1, vi(n+1, 1e8));
  dp[0][0] = 0;
  repeq(i,n) {
    repeq(j,n) {
      if (i) chmin(dp[i][j], dp[i-1][j] + cost[0][i][j]);
      if (j) chmin(dp[i][j], dp[i][j-1] + cost[1][j][i]);
    }
  }

  cout << dp[n][n] << endl;
}


/* -------- <programs end> -------- */


signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  solve();
  return 0;
}


Measured memory_bytes: 49408