/* ---------- STL Libraries ---------- */

// IO library
#include <cstdio>
#include <fstream>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm library
#include <algorithm>
#include <cmath>
#include <numeric>
#include <random>

// container library
#include <array>
#include <bitset>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>

/* ---------- Namespace ---------- */

using namespace std;

/* ---------- Type Abbreviation ---------- */

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

using ll = long long;

#define fst first
#define snd second
#define mp make_pair
#define mt make_tuple

/* ---------- conversion ---------- */

#define INT(c) static_cast<int>(c)
#define CHAR(n) static_cast<char>(n)
#define LL(n) static_cast<ll>(n)
#define DOUBLE(n) static_cast<double>(n)

/* ---------- container ---------- */

#define ALL(v) (v).begin(), (v).end()
#define SIZE(v) (LL((v).size()))

#define FIND(v, k) (v).find(k) != (v).end()
#define VFIND(v, k) find(ALL(v), k) != (v).end()

#define gsort(b, e) sort(b, e, greater<decltype(*b)>())

/* ----------- debug ---------- */

template <class T>
ostream& operator<<(ostream& os, vector<T> v) {
    os << "[";
    for (auto vv : v)
        os << vv << ",";
    return os << "]";
}

template <class T>
ostream& operator<<(ostream& os, set<T> v) {
    os << "[";
    for (auto vv : v)
        os << vv << ",";
    return os << "]";
}

template <class L, class R>
ostream& operator<<(ostream& os, pair<L, R> p) {
    return os << "(" << p.fst << "," << p.snd << ")";
}

/* ---------- Constants ---------- */

// const ll MOD = 1e9 + 7;
const int INF = 1 << 25;
// const ll INF = 1LL << 50;
// const double PI = acos(-1);
// const double EPS = 1e-10;
// mt19937 mert(LL(time(0)));

/* ---------- Short Functions ---------- */

template <typename T>
T sq(T a) {
    return a * a;
}

template <typename T>
T gcd(T a, T b) {
    if (a > b) return gcd(b, a);
    return a == 0 ? b : gcd(b % a, a);
}

template <typename T, typename U>
T mypow(T b, U n) {
    if (n == 0) return 1;
    if (n == 1) return b /* % MOD */;
    if (n % 2 == 0) {
        return mypow(b * b /* % MOD */, n / 2);
    } else {
        return mypow(b, n - 1) * b /* % MOD */;
    }
}

ll pcnt(ll b) {
    return __builtin_popcountll(b);
}

/* v-v-v-v-v-v-v-v-v Main Part v-v-v-v-v-v-v-v-v */

class BIT {
public:
    // 要素数N、値vで初期化
    explicit BIT(ll N, ll v) : V_NUM(N) {
        data.resize(N);
        fill(data.begin(), data.end(), v);
    }

    // [1, i]の総和を求める
    ll query(ll i) {
        ll ret = 0;
        while (i > 0) {
            ret += data[i];
            i -= (i & -i);
        }
        return ret;
    }

    // data[i]にv可算
    void update(ll i, ll v) {
        while (i < V_NUM) {
            data[i] += v;
            i += (i & -i);
        }
    }

    ll V_NUM;
    vector<ll> data;
};

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

    int a[N * 2];
    char c[N * 2];
    for (int i = 0; i < N * 2; ++i) {
        cin >> c[i] >> a[i];
    }

    int ww[N + 1], bb[N + 1];
    ww[0] = bb[0] = 0;
    // ww[i] = 白iより手前にある白i+xの数(x > 0)

    int wb[N + 1][N + 1], bw[N + 1][N + 1];
    fill(wb[0], wb[0] + N + 1, 0);
    fill(bw[0], bw[0] + N + 1, 0);
    // wb[i][j] = 白iより手前にある黒j+xの数(x > 0)

    BIT white(N + 1, 0), black(N + 1, 0);
    // white[i] = 白i以下がいくつ出てきたか

    for (int i = 0; i < N * 2; ++i) {
        if (c[i] == 'W') {
            ww[a[i]] = white.query(N) - white.query(a[i]);
            wb[a[i]][0] = black.query(N);
            for (int j = 1; j <= N; ++j) {
                wb[a[i]][j] = black.query(N) - black.query(j);
            }
            white.update(a[i], 1);
        } else {
            bb[a[i]] = black.query(N) - black.query(a[i]);
            bw[a[i]][0] = white.query(N);
            for (int j = 1; j <= N; ++j) {
                bw[a[i]][j] = white.query(N) - white.query(j);
            }
            black.update(a[i], 1);
        }
    }

    int dp[N + 1][N + 1];
    fill(dp[0], dp[N + 1], INF);
    dp[0][0] = 0;
    // dp[w][b] = 白i、黒jを並べる最小コスト

    for (int w = 0; w <= N; ++w) {
        for (int b = 0; b <= N; ++b) {
            if (w < N) dp[w + 1][b] = min(dp[w + 1][b], dp[w][b] + ww[w + 1] + wb[w + 1][b]);
            if (b < N) dp[w][b + 1] = min(dp[w][b + 1], dp[w][b] + bb[b + 1] + bw[b + 1][w]);
        }
    }

    cout << dp[N][N] << endl;
    return 0;
}


Measured memory_bytes: 47232