#include <bits/stdc++.h>

using namespace std;

#define int long long
// #define double long double
#define FOR(i, a, b) for(ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for(ll i = (a); i > (b); --i)
#define REP(i, n) for(ll i = 0; i < (n); ++i)
#define REPR(i, n) for(ll i = n; i >= 0; i--)
#define FOREACH(x, a) for(auto &(x) : (a))
#define VECCIN(x)                                                              \
    for(auto &youso_ : (x)) cin >> youso_
#define bitcnt(x) __builtin_popcount(x)
#define lbit(x) __builtin_ffsll(x)
#define rbit(x) __builtin_clzll(x)
#define SZ(x) ((ll)(x).size())
#define fi first
#define se second
#define All(a) (a).begin(), (a).end()
#define rAll(a) (a).rbegin(), (a).rend()

template <typename T = long long> inline T IN() {
    T x;
    cin >> x;
    return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&... tail) {
    cin >> head;
    CIN(move(tail)...);
}
#define CCIN(...)                                                              \
    char __VA_ARGS__;                                                          \
    CIN(__VA_ARGS__)
#define DCIN(...)                                                              \
    double __VA_ARGS__;                                                        \
    CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
    ll __VA_ARGS__;                                                            \
    CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
    string __VA_ARGS__;                                                        \
    CIN(__VA_ARGS__)
#define Yes(a) cout << (a ? "Yes" : "No") << "\n"
#define YES(a) cout << (a ? "YES" : "NO") << "\n"
#define Printv(v)                                                              \
    {                                                                          \
        FOREACH(x, v) { cout << x << " "; }                                    \
        cout << "\n";                                                          \
    }
template <typename T = string> inline void eputs(T s) {
    cout << s << "\n";
    exit(0);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
    std::fill((T *)array, (T *)(array + N), val);
}

template <typename T> using PQG = priority_queue<T, vector<T>, greater<T>>;
template <typename T> using PQ = priority_queue<T>;

typedef long long ll;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<ll, ll> PL;
typedef vector<PL> VPL;
typedef vector<bool> VB;
typedef vector<double> VD;
typedef vector<string> VS;

const int INF = 1e9;
const int MOD = 1e9 + 7;
// const int MOD = 998244353;
const ll LINF = 2e18;
// const double PI = atan(1.0) * 4.0;
const ll dx[] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
#define PI 3.141592653589793238

ll N, a[4040], wsum[2020][2020], bsum[2020][2020], wpos[2020], bpos[2020], dp[2020][2020];
char c[2020];

ll calcdp(ll w, ll b) {
    if(w == N && b == N) return 0;
    if(dp[w][b] != -1) return dp[w][b];
    ll &res = dp[w][b] = LINF;
    if(w < N) res = min(res, calcdp(w + 1, b) + wsum[w][b]);
    if(b < N) res = min(res, calcdp(w, b + 1) + bsum[b][w]);
    return res;
}

signed main() {
    cin >> N;
    REP(i, 2 * N) {
        cin >> c[i] >> a[i], a[i]--;
        if(c[i] == 'W')
            wpos[a[i]] = i;
        else
            bpos[a[i]] = i;
    }
    REP(i, N) FOR(j, i + 1, N) {
        if(wpos[j] < wpos[i]) wsum[i][N]++;
        if(bpos[j] < bpos[i]) bsum[i][N]++;
    }
    REP(i, N) REPR(j, N - 1) {
        wsum[i][j] = wsum[i][j + 1] + (bpos[j] < wpos[i]);
        bsum[i][j] = bsum[i][j + 1] + (wpos[j] < bpos[i]);
    }
    Fill(dp, -1);
    cout << calcdp(0, 0) << "\n";
}


Measured memory_bytes: 95744