#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...)); }
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> bord(n + 1), word(n + 1);
    for (usize bi = 0; bi <= b; bi++) { bord[bs[bi]] = bi; }
    for (usize wi = 0; wi <= w; wi++) { word[ws[wi]] = wi; }
    for (usize wi = 0; wi <= w; wi++) {
        const usize wpos = winv[ws[wi]];
        for (usize j = wpos; j < 2 * n; j++) {
            if (c[j]) {
                if (a[j] < ws[wi]) { wcost[wi][0]++; }
            } else {
                const usize bo = bord[a[j]];
                wcost[wi][bo + 1]++;
            }
        }
        for (usize bi = 1; bi <= b; bi++) { wcost[wi][bi] += wcost[wi][bi - 1]; }
    }
    for (usize bi = 0; bi <= w; bi++) {
        const usize bpos = binv[bs[bi]];
        for (usize j = bpos; j < 2 * n; j++) {
            if (c[j]) {
                const usize wo = word[a[j]];
                bcost[wo + 1][bi]++;
            } else {
                if (a[j] < bs[bi]) { bcost[0][bi]++; }
            }
        }
        for (usize wi = 1; wi <= w; wi++) { bcost[wi][bi] += bcost[wi - 1][bi]; }
    }

    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]; }
    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: 94464