#include <bits/stdc++.h>
// created [2019/11/10] 22:27:30
#pragma GCC diagnostic ignored "-Wsign-compare"
#pragma GCC diagnostic ignored "-Wsign-conversion"

using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
using uint = unsigned int;
using usize = std::size_t;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<typename T> constexpr T popcount(const T u) { return u ? static_cast<T>(__builtin_popcountll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T log2p1(const T u) { return u ? static_cast<T>(64 - __builtin_clzll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T msbp1(const T u) { return log2p1(u); }
template<typename T> constexpr T lsbp1(const T u) { return __builtin_ffsll(u); }
template<typename T> constexpr T clog(const T u) { return u ? log2p1(u - 1) : static_cast<T>(u); }
template<typename T> constexpr bool ispow2(const T u) { return u and (static_cast<u64>(u) & static_cast<u64>(u - 1)) == 0; }
template<typename T> constexpr T ceil2(const T u) { return static_cast<T>(1) << clog(u); }
template<typename T> constexpr T floor2(const T u) { return u == 0 ? static_cast<T>(0) : static_cast<T>(1) << (log2p1(u) - 1); }
template<typename T> constexpr bool btest(const T mask, const usize ind) { return static_cast<bool>((static_cast<u64>(mask) >> ind) & static_cast<u64>(1)); }
template<typename T> void bset(T& mask, const usize ind) { mask |= (static_cast<T>(1) << ind); }
template<typename T> void breset(T& mask, const usize ind) { mask &= ~(static_cast<T>(1) << ind); }
template<typename T> void bflip(T& mask, const usize ind) { mask ^= (static_cast<T>(1) << ind); }
template<typename T> void bset(T& mask, const usize ind, const bool b) { (b ? bset(mask, ind) : breset(mask, ind)); }
template<typename T> constexpr T bcut(const T mask, const usize ind) { return ind == 0 ? static_cast<T>(0) : static_cast<T>((static_cast<u64>(mask) << (64 - ind)) >> (64 - ind)); }
template<typename T> bool chmin(T& a, const T& b) { return (a > b ? a = b, true : false); }
template<typename T> bool chmax(T& a, const T& b) { return (a < b ? a = b, true : false); }
constexpr unsigned int mod                  = 1000000007;
template<typename T> constexpr T inf_v      = std::numeric_limits<T>::max() / 4;
template<typename Real> constexpr Real pi_v = Real{3.141592653589793238462643383279502884};

template<typename T>
T read()
{
    T v;
    return std::cin >> v, v;
}
template<typename T, typename... Args>
auto read(const usize size, Args... args)
{
    std::vector<decltype(read<T>(args...))> ans(size);
    for (usize i = 0; i < size; i++) { ans[i] = read<T>(args...); }
    return ans;
}
template<typename... Types>
auto reads() { return std::tuple<std::decay_t<Types>...>{read<Types>()...}; }
#    define SHOW(...) static_cast<void>(0)

template<typename T>
std::vector<T> make_v(const usize size, const T v) { return std::vector<T>(size, v); }
template<typename... Args>
auto make_v(const usize size, Args... args) { return std::vector<decltype(make_v(args...))>(size, make_v(args...)); }

template<usize lg>
class wavelet_matrix
{
public:
    using value_type = u64;
    template<typename InIt>
    wavelet_matrix(const InIt first, const InIt last) : sz{static_cast<usize>(std::distance(first, last))}
    {
        for (usize i = 0; i < lg; i++) { zero[i] = 0, table[i] = fid(sz); }
        std::vector<value_type> v{first, last};
        std::vector<value_type> z(sz), o(sz);
        usize zn = 0, on = 0;
        for (usize d = 0; d < lg; d++) {
            zn = 0, on = 0;
            for (usize i = 0; i < sz; i++) {
                const bool b = btest(v[i], lg - d - 1);
                table[d].set(i, b), (b ? o[on++] : z[zn++]) = v[i];
            }
            table[d].build(), zero[d] = zn, std::swap(v, z);
            for (usize i = 0; i < on; i++) { v[zn + i] = o[i]; }
        }
    }
    usize less_than(usize l, usize r, const value_type v) const
    {
        assert(l <= r);
        usize ans = 0;
        for (usize i = 0; i < lg; i++) {
            const usize zl = table[i].zero(l), zr = table[i].zero(r), z = zero[i];
            if (btest(v, lg - i - 1)) {
                ans += zr - zl, l += z - zl, r += z - zr;
            } else {
                l = zl, r = zr;
            }
        }
        return ans;
    }
    usize range_freq(const usize l, const usize r, const value_type vmin, const value_type vsup) const { return less_than(l, r, vsup) - less_than(l, r, vmin); }
    value_type quantile(usize l, usize r, usize n) const
    {
        assert(l <= r), assert(r - l > n);
        value_type ans = 0;
        for (usize i = 0; i < lg; i++) {
            const usize zl = table[i].zero(l), zr = table[i].zero(r), z = zero[i];
            if (n >= zr - zl) {
                ans += value_type(1) << (lg - i - 1), l += z - zl, r += z - zr, n -= (zr - zl);
            } else {
                l = zl, r = zr;
            }
        }
        return ans;
    }

private:
    static constexpr usize bucket_size = sizeof(value_type) * 8;
    static constexpr usize bslog       = log2p1(bucket_size) - 1;
    static constexpr usize wind(const usize n) { return n >> (bslog); }
    static constexpr usize bind(const usize n) { return bcut(n, bslog); }
    class fid
    {
    private:
        usize sz, bn;
        std::vector<value_type> data;
        std::vector<usize> large;

    public:
        fid() : sz{0} {}
        fid(const usize b) : sz{b}, bn{wind(sz) + 2}, data(bn, 0), large(bn, 0) {}
        void build()
        {
            for (usize i = 1; i < large.size(); i++) { large[i] = large[i - 1] + popcount(data[i - 1]); }
        }
        bool operator[](const usize n) const { return btest(data[wind(n)], bind(n)); }
        void set(const usize n, const bool b) { bset(data[wind(n)], bind(n), b); }
        usize one(const usize n) const { return large[wind(n)] + popcount(bcut(data[wind(n)], bind(n))); }
        usize zero(const usize n) const { return n - one(n); }
    };
    const usize sz;
    std::array<usize, lg> zero;
    std::array<fid, lg> table;
};
int main()
{
    const auto n = read<int>();
    std::vector<bool> c(2 * n);
    std::vector<usize> a(2 * n);
    std::vector<usize> bs, ws;
    usize w = 0, b = 0;
    for (usize i = 0; i < 2 * n; i++) {
        c[i] = (read<char>() == 'W'), a[i] = read<int>() - 1;
        if (c[i]) {
            w++, ws.push_back(a[i]);
        } else {
            b++, bs.push_back(a[i]);
        }
    }
    ws.push_back(n), bs.push_back(n);
    std::sort(ws.begin(), ws.end()), std::sort(bs.begin(), bs.end());
    std::vector<usize> binv(n + 1), winv(n + 1);  // (b_i)の場所,(w_i)の場所
    for (usize i = 0; i < 2 * n; i++) { (c[i] ? winv : binv)[a[i]] = i; }
    auto wcost = make_v(w + 1, b + 1, 0UL);  // wcost[i][j] = 元の場所でw_iより右の[b_0,b_j),[w_0,w_i)の個数
    auto bcost = make_v(w + 1, b + 1, 0UL);  // bcost[i][j] = 元の場所でb_jより右の[b_0,b_j),[w_0,w_i)の個数
    std::vector<usize> bvs(2 * n, n), wvs(2 * n, n);
    for (usize i = 0; i < 2 * n; i++) { (c[i] ? wvs : bvs)[i] = a[i]; }
    wavelet_matrix<12> wwm(wvs.begin(), wvs.end());
    wavelet_matrix<12> bwm(bvs.begin(), bvs.end());
    for (usize wi = 0; wi <= w; wi++) {
        const usize wpos = winv[ws[wi]];
        wcost[wi][0]     = wwm.less_than(wpos, 2 * n, ws[wi]);
        for (usize bi = 1; bi <= b; bi++) {
            wcost[wi][bi] = wcost[wi][0] + bwm.less_than(wpos, 2 * n, bs[bi]);
        }
    }
    for (usize bi = 0; bi <= w; bi++) {
        const usize bpos = binv[bs[bi]];
        bcost[0][bi]     = bwm.less_than(bpos, 2 * n, bs[bi]);
        for (usize wi = 1; wi <= w; wi++) {
            bcost[wi][bi] = bcost[0][bi] + wwm.less_than(bpos, 2 * n, ws[wi]);
        }
    }

    auto dp  = make_v(w + 1, b + 1, inf_v<usize>);
    dp[0][0] = 0;
    for (usize wi = 0; wi <= w; wi++) {
        for (usize bi = 0; bi <= b; bi++) {
            if (wi + 1 <= w) { chmin(dp[wi + 1][bi], dp[wi][bi] + wcost[wi][bi]); }
            if (bi + 1 <= b) { chmin(dp[wi][bi + 1], dp[wi][bi] + bcost[wi][bi]); }
        }
    }
    std::cout << dp[w][b] << std::endl;
    return 0;
}


Measured memory_bytes: 94592