#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <random>
#include <tuple>
#include <iomanip>
#include <cstring>

using namespace std;

typedef long long ll;
//typedef pair<int,int> Pint;
//typedef pair<ll, ll> P;
typedef pair<ll, pair<ll, ll>> P;
//typedef tuple<int,int,int> T;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define revrep(i, n) for(ll i = (n-1); i >= 0; i--)
#define pb push_back
#define f first
#define s second
const ll INFL = 1LL << 60;//10^18 = 2^60
const int INF = 1 << 30;//10^9
const ll MOD = 1e9 + 7;
//const ll MOD  = 998244353;
//ll MOD;
vector<ll> dy = {0, 0, 1, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, -1, 0, 0, 1, -1, 1, -1, 0};

ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}
ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}
ll inverse(ll x){return pow_mod(x, MOD - 2);};

//最大公約数
ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

//最小公倍数
ll lcm(ll x, ll y){return x / gcd(x, y) * y;};

//コンビネーション
const int MAXcomb = 200010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}

//約数の列挙O(√n)
vector<ll> divisor(ll n){
    vector<ll> res(0);
    for(ll i = 1; i * i <= n; i++){
        if(n % i == 0){
            res.push_back(i);
            if(i != n/i) res.push_back(n/i);
        }
    }
    sort(res.begin(), res.end());
    return res;
}

int main(){
  ll N;
  cin >> N;
  vector<char> col(2 * N);
  vector<ll> num(2 * N);
  rep(i, 2 * N){
    cin >> col[i] >> num[i];
    num[i]--;
  }
  ll white[N][N+1];
  ll black[N][N+1];
  rep(i, N)rep(j, N){
    white[i][j] = 0;
    black[i][j] = 0;
  }

  ll cntW = 0, cntB = 0;
  ll usedW[N], usedB[N];
  rep(i, N){
    usedW[i] = 0;
    usedB[i] = 0;
  }

  rep(i, 2 * N){
    char c = col[i];
    ll n = num[i];
    if(c == 'W'){
      usedW[n] = 1;
      cntW++;
    }else{
      usedB[n] = 1;
      cntB++;
    }
    vector<ll> sumW(N+1, 0), sumB(N+1, 0);
    rep(i, N){
      sumW[i+1] = sumW[i] + usedW[i];
      sumB[i+1] = sumB[i] + usedB[i];
    }
    rep(i, N+1){
      if(c == 'W') white[n][i] = (cntW - sumW[n+1]) + (cntB - sumB[i]);
      else black[n][i] = (cntB - sumB[n+1]) + (cntW - sumW[i]);
    }
  }


  ll dp[N+1][N+1];//前からwhite i個, black j個並べた時の最小コスト
  rep(i, N+1)rep(j, N+1) dp[i][j] = INFL;
  dp[0][0] = 0;
  for(ll i = 0; i <= N; i++){
    for(ll j = 0; j <= N; j++){
      if(i >= 1) dp[i][j] = min(dp[i][j], dp[i-1][j] + white[i-1][j]);
      if(j >= 1) dp[i][j] = min(dp[i][j], dp[i][j-1] + black[j-1][i]);
    }
  }
  cout << dp[N][N] << endl;
}


Measured memory_bytes: 94208