using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text;
using System.Diagnostics;
using System.Numerics;
using static System.Console;
using static System.Convert;
using static System.Math;
using static Template;
using Pi = Pair<int, int>;

class Solver
{
    int[][] ctw, ctb;
    int[] invw, invb;
    Pi[] rw,rb;

    public void Solve(Scanner sc)
    {
        var N = sc.Int;
        ctw = Create(N+1,()=>new int[N+1]); ctb=Create(N+1,()=>new int[N+1]); //iが書かれているボールよりも左にある、jより大きいの数が書かれている自分とは違う色のボールが何個あるか
        invw = new int[N + 1]; invb = new int[N + 1];//各色での転倒数
        rw = new Pi[N+1]; rb = new Pi[N + 1];
        rw[0] = new Pi(-1, 0);
        rb[0] = new Pi(-1, 0);
        for (int i = 0; i < N * 2; i++)
        {
            char c; int a;
            sc.Make(out c, out a); 
            if (c == 'W')
            {
                rw[a] = new Pi(i, a);
            }
            else
            {
                rb[a] = new Pi(i, a);
            }
        }
        Array.Sort(rw, (a, b) => a.v1 - b.v1);
        Array.Sort(rb, (a, b) => a.v1 - b.v1);
        InversionNumber(rw.Skip(1).Select(v => v.v2).ToArray(), invw);
        InversionNumber(rb.Skip(1).Select(v => v.v2).ToArray(), invb);
        {
            var idx = 0;
            var use = new bool[N + 1];
            for (int i = 1; i <= N; i++)
            {
                while (idx <= N && rb[idx].v1 < rw[i].v1)
                {
                    use[rb[idx].v2] = true;
                    idx++;
                }
                var ct = 0;
                for (int j = N - 1; j >= 0; j--)
                {
                    ct += ToInt32(use[j + 1]);
                    ctw[rw[i].v2][j] = ct;
                }
            }
        }
        {
            var idx = 0;
            var use = new bool[N + 1];
            for (int i = 1; i <= N; i++)
            {
                while (idx <= N && rw[idx].v1 < rb[i].v1)
                {
                    use[rw[idx].v2] = true;
                    idx++;
                }
                var ct = 0;
                for (int j = N - 1; j >= 0; j--)
                {
                    ct += ToInt32(use[j + 1]);
                    ctb[rb[i].v2][j] = ct;
                }
            }
        }
        //白をi個,黒をj個並べたときの最小値
        var dp = Create(N + 1, () => Create(N+1,()=>int.MaxValue/2));
        dp[0][0] = 0;
        for (int i = 0; i <= N; i++)
            for (int j = 0; j <= N; j++)
            {
                if (i > 0)
                {
                    chmin(ref dp[i][j], dp[i - 1][j] + invw[i] + ctw[i][j]);
                }
                if (j > 0)
                {
                    chmin(ref dp[i][j], dp[i][j - 1] + invb[j] + ctb[j][i]);
                }
            }
        WriteLine(dp[N][N]);
    }
    public static long InversionNumber(int[] A,int[] ct)
    {
        var bit = new BIT(A.Length + 1);
        var res = 0L;
        for (var i = 0; i < A.Length; i++)
        {
            var t = bit[A[i]];
            t = i - t;
            bit.add(A[i], 1);
            ct[A[i]] = (int)t;
            res += t;
        }
        return res;
    }
}

public class BIT
{
    //1-indexed
    long[] data;
    public BIT(int num)
    {
        data = new long[num + 1];
    }
    public long this[int index]
    {
        get { var s = 0L; for (var i = index; i > 0; i -= i & -i) s += data[i]; return s; }
    }
    public void add(int index, long value)
    {
        for (var i = index; i < data.Length; i += i & -i) data[i] += value;
    }
}
#region Template
public static class Template
{
    static void Main(string[] args)
    {
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        new Solver().Solve(new Scanner());
        Console.Out.Flush();
    }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool chmin<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) == 1) { a = b; return true; } return false; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool chmax<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) == -1) { a = b; return true; } return false; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static void swap<T>(ref T a, ref T b) { var t = b; b = a; a = t; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static void swap<T>(this IList<T> A, int i, int j) { var t = A[i]; A[i] = A[j]; A[j] = t; }
    public static T[] Shuffle<T>(this IList<T> A) { T[] rt = A.ToArray(); Random rnd = new Random(); for (int i = rt.Length - 1; i >= 1; i--) swap(ref rt[i], ref rt[rnd.Next(i + 1)]); return rt; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T[] Create<T>(int n, Func<T> f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(); return rt; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T[] Create<T>(int n, Func<int, T> f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(i); return rt; }
    public static void Fail<T>(T s) { Console.WriteLine(s); Console.Out.Close(); Environment.Exit(0); }

}
public class Scanner
{
    public string Str => Console.ReadLine().Trim();
    public int Int => int.Parse(Str);
    public long Long => long.Parse(Str);
    public double Double => double.Parse(Str);
    public int[] ArrInt => Str.Split(' ').Select(int.Parse).ToArray();
    public long[] ArrLong => Str.Split(' ').Select(long.Parse).ToArray();
    public char[][] Grid(int n) => Create(n, () => Str.ToCharArray());
    public int[] ArrInt1D(int n) => Create(n, () => Int);
    public long[] ArrLong1D(int n) => Create(n, () => Long);
    public int[][] ArrInt2D(int n) => Create(n, () => ArrInt);
    public long[][] ArrLong2D(int n) => Create(n, () => ArrLong);
    private Queue<string> q = new Queue<string>();
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public T Next<T>() { if (q.Count == 0) foreach (var item in Str.Split(' ')) q.Enqueue(item); return (T)Convert.ChangeType(q.Dequeue(), typeof(T)); }
    public void Make<T1>(out T1 v1) => v1 = Next<T1>();
    public void Make<T1, T2>(out T1 v1, out T2 v2) { v1 = Next<T1>(); v2 = Next<T2>(); }
    public void Make<T1, T2, T3>(out T1 v1, out T2 v2, out T3 v3) { Make(out v1, out v2); v3 = Next<T3>(); }
    public void Make<T1, T2, T3, T4>(out T1 v1, out T2 v2, out T3 v3, out T4 v4) { Make(out v1, out v2, out v3); v4 = Next<T4>(); }
    public void Make<T1, T2, T3, T4, T5>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5) { Make(out v1, out v2, out v3, out v4); v5 = Next<T5>(); }
    public void Make<T1, T2, T3, T4, T5, T6>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6) { Make(out v1, out v2, out v3, out v4, out v5); v6 = Next<T6>(); }
    //public (T1, T2) Make<T1, T2>() { Make(out T1 v1, out T2 v2); return (v1, v2); }
    //public (T1, T2, T3) Make<T1, T2, T3>() { Make(out T1 v1, out T2 v2, out T3 v3); return (v1, v2, v3); }
    //public (T1, T2, T3, T4) Make<T1, T2, T3, T4>() { Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4); return (v1, v2, v3, v4); }
}
public class Pair<T1, T2> : IComparable<Pair<T1, T2>>
{
    public T1 v1;
    public T2 v2;
    public Pair() { }
    public Pair(T1 v1, T2 v2)
    { this.v1 = v1; this.v2 = v2; }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int CompareTo(Pair<T1, T2> p)
    {
        var c = Comparer<T1>.Default.Compare(v1, p.v1);
        if (c == 0)
            c = Comparer<T2>.Default.Compare(v2, p.v2);
        return c;
    }
    public override string ToString() => $"{v1.ToString()} {v2.ToString()}";
    public void Deconstruct(out T1 a, out T2 b) { a = v1; b = v2; }
}

public class Pair<T1, T2, T3> : Pair<T1, T2>, IComparable<Pair<T1, T2, T3>>
{
    public T3 v3;
    public Pair() : base() { }
    public Pair(T1 v1, T2 v2, T3 v3) : base(v1, v2)
    { this.v3 = v3; }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int CompareTo(Pair<T1, T2, T3> p)
    {
        var c = base.CompareTo(p);
        if (c == 0)
            c = Comparer<T3>.Default.Compare(v3, p.v3);
        return c;
    }
    public override string ToString() => $"{base.ToString()} {v3.ToString()}";
    public void Deconstruct(out T1 a, out T2 b, out T3 c) { Deconstruct(out a, out b); c = v3; }
}
#endregion

Measured memory_bytes: 62032