#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
    bool done_something = false;
    stringstream res;
    res << "[";
    for (; begin_iter != end_iter and counter; ++begin_iter) {
        done_something = true;
        counter--;
        res << *begin_iter << ", ";
    }
    string str = res.str();
    if (done_something) {
        str.pop_back();
        str.pop_back();
    }
    str += "]";
    return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
    vector<int> ord(size);
    for (int i = 0; i < size; i++) ord[i] = i;
    sort(ord.begin(), ord.end(), compare);
    return ord;
}

template <typename T>
bool MinPlace(T& a, const T& b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template <typename T>
bool MaxPlace(T& a, const T& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <typename Container>
int SZ(const Container& S) { return S.size(); }

template <typename S, typename T>
ostream& operator <<(ostream& out, const pair<S, T>& p) {
    out << "{" << p.first << ", " << p.second << "}";
    return out;
}

template <typename T>
ostream& operator <<(ostream& out, const vector<T>& v) {
    out << "[";
    for (int i = 0; i < (int)v.size(); i++) {
        out << v[i];
        if (i != (int)v.size()-1) out << ", ";
    }
    out << "]";
    return out;
}

#if DEBUG && !ONLINE_JUDGE
    ifstream input_from_file("input.txt");
    #define cin input_from_file

    #define dbg_var(x) clog << #x  << ": " << x << endl;
    #define dbg_array(x, len) clog << #x << ": " << print_iterable(x, x+len, -1) << endl;
#else
    #define dbg_var(x)
    #define dbg_array(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

const int MAXN = 2010;
int cw[MAXN][MAXN];
int cb[MAXN][MAXN];
int ccw[MAXN], ccb[MAXN];
int din[MAXN][MAXN];

char c[MAXN*2];
int a[MAXN*2];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); // Remove in problems with online queries!
    int N;
    cin >> N;
    for (int i = 1; i <= 2*N; i++) cin >> c[i] >> a[i];
    for (int j = 0; j <= N; j++) {
        int black_num = 0;
        int white_num = 0;
        for (int it = 2*N; it >= 1; it--) {
            if (c[it] == 'W') {
                cw[a[it]][j] = black_num;
                if (a[it] == j+1) ccw[a[it]] = white_num;
                white_num += (a[it] <= j);
            } else if (c[it] == 'B') {
                cb[a[it]][j] = white_num;
                black_num += (a[it] <= j);
                if (a[it] == j+1) ccb[a[it]] = black_num;
            }
        }
    }
    // for (int j = 0; j <= N; j++) {
        // dbg_var(j);
        // for (int i = 1; i <= N; i++) cout << cw[i][j] << "\n";
    // }
    // return 0;
    for (int i = 0; i <= N; i++) for (int j = 0; j <= N; j++) {
        if (i == 0 and j == 0) continue;
        if (i == 0) din[i][j] = din[i][j-1] + cb[j][i] + ccb[j];
        else if (j == 0) din[i][j] = din[i-1][j] + cw[i][j] + ccw[i];
        else din[i][j] = min(din[i][j-1] + cb[j][i] + ccb[j],
                             din[i-1][j] + cw[i][j] + ccw[i]);
    }
    cout << din[N][N] << "\n";
}



Measured memory_bytes: 47616