#define STOPIT
#include <bits/stdc++.h>
#define loop(n) for (lint ngtkana_is_a_genius = 0; ngtkana_is_a_genius < lint(n); ngtkana_is_a_genius++)
#define rep(i, begin, end) for (lint i = lint(begin); (i) < lint(end); i++)
#define all(v) v.begin(), v.end()
#define rand(l, r) std::uniform_int_distribution<>(l, r)(mt)
using lint = long long;
auto mt = std::mt19937_64(std::random_device{}());
auto cmn = [](auto&& a, auto b){ if (a > b) {a = b; return true;} return false; };
auto cmx = [](auto&& a, auto b){ if (a < b) {a = b; return true;} return false; };
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) { std::cerr << " " << head; debug_impl(tail...); }
#ifndef STOPIT
#define debug(...)\
  do {\
    std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";\
    debug_impl(__VA_ARGS__);\
    std::cerr << std::noboolalpha;\
  } while (false)
#else
#define debug(...) {}
#endif

template <class Seg, class SegPtr>
struct segment_tree_entry;

template <class Seg, class SegPtr, class Pointer, class Reference>
struct segment_tree_iterator;

template <typename Value, typename BinaryOp>
class segment_tree {
public:
  using value_type = Value;
  using this_type = segment_tree<Value, BinaryOp>;
  using entry_type = segment_tree_entry<this_type, this_type*>;
  using const_entry_type = segment_tree_entry<this_type, this_type const*>;
  using iterator = segment_tree_iterator<this_type, this_type*, value_type*, value_type&>;
  using const_iterator = segment_tree_iterator<this_type, this_type const*, value_type const*, value_type const&>;

friend class segment_tree_entry<this_type, this_type*>;
friend class segment_tree_entry<this_type, this_type const*>;

private:
  int                  sz, n, N;
  BinaryOp             op;
  Value                id;
  std::vector< Value > table;

  auto& op_assign(Value& x, Value y) const
    { return x = op(x, y); }
  void merge(int u)
    { table.at(u) = op(table.at(2 * u), table.at(2 * u + 1)); }

public:
  segment_tree(int sz, BinaryOp op, Value id):
    sz(sz), n(std::pow(2, int(std::log2(2*sz-1)))), N(n * 2), op(op), id(id), table (N, id) {}

  iterator begin()
    { return iterator(this, 0); }

  iterator end()
    { return iterator(this, sz); }

  const_iterator begin() const
    { return const_iterator(this, 0); }

  const_iterator end() const
    { return const_iterator(this, sz); }

  auto at(std::size_t i)
    { return entry_type(this, i); }

  auto at(std::size_t i) const
    { return table.at(n + i); }

  auto& lazy_at(std::size_t i)
    { return table.at(n + i); }

  auto& lazy_at(std::size_t i) const
    { return table.at(n + i); }

  auto collect() const {
    auto ret = std::vector<Value>(sz);
    for (auto i = 0; i < sz; i++)
      { ret.at(i) = at(i); }
    return ret;
  }

  auto query(int l, int r) const {
    auto const dfs = [&](auto&& f, int l, int r, int k, int L, int R) -> Value {
      return l <= L && R <= r ? table.at(k)
        : R <= l || r <= L ? id
        : op(f(f, l, r, 2*k, L, (L+R)/2), f(f, l, r, 2*k+1, (L+R)/2, R));
    };
    return dfs(dfs, l, r, 1, 0, n);
  }

  void build()
    { for (auto i = n - 1; i > 0; i--) merge(i); }
};

template <class Seg, class SegPtr>
class segment_tree_entry {
  using value_type = typename Seg::value_type;
  SegPtr seg;
  std::size_t i;

  auto& get()
    { return seg->table.at(seg->n + i); }

  void build_oneline(int i)
    { for (i += seg->n, i /= 2; i > 0; i /= 2) seg->merge(i); }

public:
  segment_tree_entry(SegPtr seg, std::size_t i) : seg(seg), i(i) {}

  operator value_type() {
    return seg->table.at(seg->n + i);
  }
  void operator=(value_type x) {
    seg->table.at(seg->n + i) = x;
    build_oneline(i);
  }
  void operator+=(value_type x) {
    seg->table.at(seg->n + i) += x;
    build_oneline(i);
  }
  void operator-=(value_type x) {
    seg->table.at(seg->n + i) += x;
    build_oneline(i);
  }
  void operator*=(value_type x) {
    seg->table.at(seg->n + i) += x;
    build_oneline(i);
  }
  void operator/=(value_type x) {
    seg->table.at(seg->n + i) += x;
    build_oneline(i);
  }
};

template <class Seg, class SegPtr, class Pointer, class Reference>
class segment_tree_iterator {
  using this_type = segment_tree_iterator<Seg, SegPtr, Pointer, Reference>;
  using value_type = typename Seg::value_type;
  using pointer = Pointer;
  using reference = Reference;

  template <class Seg_, class SegPtr_, class Pointer_, class Reference_>
  friend bool operator!=(segment_tree_iterator<Seg_, SegPtr_, Pointer_, Reference_>, segment_tree_iterator<Seg_, SegPtr_, Pointer_, Reference_>);

  SegPtr seg;
  std::size_t i;

public:
  segment_tree_iterator(SegPtr seg, std::size_t i) : seg(seg), i(i) {}

  this_type& operator++(){ i++; return *this; }
  this_type  operator++(int){ auto old = *this; ++i; return old; }
  pointer operator->(){ return &seg->at(i); }
  value_type operator*(){ return seg->at(i); }
};

template <class Seg, class SegPtr, class Pointer, class Reference>
bool operator!=(segment_tree_iterator<Seg, SegPtr, Pointer, Reference> a, segment_tree_iterator<Seg, SegPtr, Pointer, Reference> b) {
  return a.i != b.i;
}

template<typename Value, typename BinaryOp>
auto make_segment_tree(int sz, BinaryOp const& op, Value id)
  { return segment_tree<Value, BinaryOp>(sz, op, id); }

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr>
std::istream& operator>> (std::istream& is, Container& v)
  { for (auto & x : v) { is >> x; } return is; }

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr >
std::ostream& operator<< (std::ostream& os, Container const& v) {
 os << "{";
  for (auto it = v.begin(); it != v.end(); it++)
    {os << (it != v.begin() ? "," : "") << *it;}
  return os << "}";
}

template <typename T>
auto make_vector_impl(size_t sz, T t) {return std::vector<T>(sz, t);}

template <size_t N, typename T, typename U, std::enable_if_t<N == 1, std::nullptr_t> = nullptr>
auto make_vector(size_t sz, U u) {return make_vector_impl(sz, T(u));}

template <size_t N, typename T, std::enable_if_t<N == 1, std::nullptr_t> = nullptr>
auto make_vector(size_t sz) {return std::vector<T>(sz);}

template <size_t N, typename T, typename... Args, std::enable_if_t<N != 1, std::nullptr_t> = nullptr>
auto make_vector(size_t a, Args... args) {return make_vector_impl(a, make_vector<N - 1, T>(args...));}

template <typename T, typename Size_t>
auto& at(T& t, Size_t i) {return t.at(i);}

template <typename T, typename Size_t, typename... Args>
auto& at(T& t, Size_t i, Args... args) {return at(t.at(i), args...);}

// require gcc >= 7.1.0
template < class ... Keys >
class fmt_t {
    using storage_t = std::tuple< Keys ... >;
    storage_t storage;
    static constexpr std::size_t N = sizeof ... (Keys);

    // is_exact_match_impl
    template < std::size_t I, class Value >
      auto is_exact_match_impl(long, Value) const
        { return false; }

    template < std::size_t I, class Value,
      std::enable_if_t<
        std::is_same< std::decay_t< Value > , char >::value
        == std::is_same< std::tuple_element_t< I, storage_t >, char >::value,
      std::nullptr_t > = nullptr,
      class = decltype(std::declval< Value >() == std::get< I >(std::declval< storage_t >())) >
      auto is_exact_match_impl(int, Value x) const
        { return x == std::get< I >(storage); }

    template < class Value, std::size_t ... Is >
      auto find_exact_match_impl(Value x, std::integer_sequence< std::size_t, Is ... >) const {
        auto ret = false;
        (void)std::initializer_list< std::nullptr_t >
          { (ret |= is_exact_match_impl< Is >(int{}, x), nullptr) ...  };
        return ret;
      }

    template < class Value >
      auto exists_exact_match(Value x) const
      {  return find_exact_match_impl(x, std::make_index_sequence< N >()); }

    // tuple_format_impl
    template < class Tuple,  std::size_t ... Is >
    std::string tuple_format_impl(const Tuple& tuple, std::integer_sequence< std::size_t, Is ... >) const {
      std::string ret = "(";
      (void)std::initializer_list< std::nullptr_t >
        { (ret = ret + (Is == 0 ? "" : ",") + format(std::get< Is >(tuple)), nullptr) ... };
      return ret + ")";
    }

    // usual_format
    template < class Value >
    std::string usual_format(long, Value x) const
      { return std::to_string(x); }

    template < class Value, std::enable_if_t< std::is_same< std::decay_t< Value >, char >::value, std::nullptr_t > = nullptr >
    std::string usual_format(int, Value c) const
      { return std::string{'\''} + std::string{c} + std::string{'\''}; }

    std::string usual_format(int, char const* s) const
      { return "\"" + std::string(s) + "\""; }

    std::string usual_format(int, std::string const s) const
      { return "\"" + s + "\""; }

    template < class Container, class = typename Container::value_type >
    std::string usual_format(int, Container const & v) const {
      return "{" + std::accumulate(v.begin(), v .end(), std::string{},
        [this](auto const& s, auto const x) { return s + (s.empty() ? "" : ",") + this->format(x); })
        + "}";
    }

    template < class Tuple, std::size_t N = std::tuple_size< Tuple >::value >
    std::string usual_format(int, Tuple const& tuple) const
      { return tuple_format_impl(tuple, std::make_index_sequence< N >()); }

    // format
    template < class Value > std::string format(Value&& x) const
      { return exists_exact_match(x) ? std::string{'_'} : usual_format(int{}, x); }

  public:
    fmt_t()=default;
    template < Keys ... > fmt_t(Keys&& ... keys ) : storage(keys ... ){}

    template < class Value > std::string operator()(Value&& x) const
      { return format(x); }
};
template < class ... Keys > auto fmt(Keys&& ... keys)
  { return fmt_t< Keys ... >(std::forward< Keys >(keys) ... ); }

int main() {
  std::cin.tie(0); std::cin.sync_with_stdio(false);
  int n; std::cin >> n;
  int N = 2 * n;
  std::vector<int> a(n),b(n);
  rep(i,0,N) {
    char c; int x; std::cin >> c >> x;
    x--;
    (c=='W' ? a : b).at(x) = i;
  }
  debug(a,b);

  int inf = std::numeric_limits<int>::max();
  auto dp = make_vector<2,int>(n+1,n+1,inf);
  at(dp,0,0) = 0;
  rep(i,0,n+1) {
    auto seg = make_segment_tree<int>(N,std::plus<>{},0);
    for (int x : std::vector<int>(a.begin(),a.begin()+i)) {
      seg.at(x) += 1;
    }
    rep(j,0,n+1) {
      int crr = at(dp,i,j);
      assert(crr != inf);
      debug(i,j,seg);
      if (i < n) {
        int x = a.at(i);
        cmn(at(dp,i+1,j), crr + x - seg.query(0,x));
      }
      if (j < n){
        int y = b.at(j);
        cmn(at(dp,i,j+1), crr + y - seg.query(0,y));
        seg.at(y) += 1;
      }
    }
  }
  #ifndef STOPIT
    rep(i,0,n+1) {
      auto&& v = dp.at(i);
      debug(i,fmt(inf)(v));
    }
  #endif
  int ans = at(dp,n,n);
  std::cout << ans << std::endl;
  return 0;
}

/*
白を i 個、黒を ｊ 個解決するための最小手数を DP です。
この状態で白を解決するためには、その位置が x とすると、
x より左で未解決なものの個数です。
そこで、解決しているものをセグツリーで管理です。
ループの内側で n 回セグツリーを作ります。
*/

Measured memory_bytes: 16000