object Main {
  def main(args: Array[String]): Unit = {
    val s = new Main()
    s.solve()
    s.out.flush()
  }
}

class Main {
  import java.io._
  import java.util.StringTokenizer

  import scala.collection.mutable
  import scala.util.Sorting
  import math.{abs, max, min}
  import mutable.{ArrayBuffer, ListBuffer}
  import scala.reflect.ClassTag

  val MOD = 1000000007
  val out = new PrintWriter(System.out)

  def solve(): Unit = {
    val N = ni()
    val P = Array.ofDim[Int](2, N + 1)
    REP(2 * N) { i =>
      val c = nc()
      val a = ni()
      val x = if (c == 'B') 0 else 1
      P(x)(a) = i + 1
    }

    val inv = Array.ofDim[Int](2, N + 1)
    REP(2) { x =>
      val bit = new BIT(2 * N, 0)(_+_)
      REP(N, 1) { i =>
        inv(x)(i) = i - 1 - bit.sum(P(x)(i))
        bit.add(P(x)(i) - 1, 1)
      }
    }

//    REP(2) { x =>
//      debug(s"inv[$x]")
//      debug(inv(x))
//    }

    val oppo = Array.ofDim[Int](2, N + 1, N + 1)
    REP(2) { x =>
      val bit = new BIT(2 * N, 0)(_+_)
      REP(N, 1) { i =>
        bit.clear()
        REP(N, 1) { j =>
          bit.add(P(x^1)(j) - 1, 1)
          oppo(x)(i)(j) = j - bit.sum(P(x)(i))
        }
      }
    }
//
//    REP(2) { x =>
//      debug(s"oppo[$x]")
//      REP(N + 1) { i =>
//        debug(oppo(x)(i))
//      }
//    }

    // i: B, j: W
    val dp = Array.fill[Int](N + 1, N + 1)(1e9.toInt)
    dp(0)(0) = 0

    REP(N + 1) { i =>
      REP(N + 1) { j =>
        if (i > 0) {
          val dest = i + j
          val cur = P(0)(i) + inv(0)(i) + oppo(0)(i)(j)
          val move = cur - dest
          dp(i)(j) = min(dp(i)(j), dp(i - 1)(j) + move)
        }
        if (j > 0) {
          val dest = i + j
          val cur = P(1)(j) + inv(1)(j) + oppo(1)(j)(i)
          val move = cur - dest
          dp(i)(j) = min(dp(i)(j), dp(i)(j - 1) + move)
        }
      }
    }

//    debug("DP")
//    REP(N + 1) { i =>
//      debug(dp(i))
//    }

    out.println(dp(N)(N))
  }


  class BIT(n: Int, zero: Int)(f: (Int, Int) => Int) {
    def this(n: Int) = this(n, 0)(_ + _)

    private val N = {
      val a = Integer.highestOneBit(n)
      if (a == n) a else a << 1
    }
    private val bit = if (zero != 0) Array.fill[Int](N + 1)(zero) else Array.ofDim[Int](N + 1)

    def clear(): Unit = {
      java.util.Arrays.fill(bit, zero)
    }

    /**
      * 1 index
      * addとindex違うよ
      * cumsumなんかといっしょ
      */
    def sum(i: Int): Int = {
      assert(i <= n)
      var x = i
      var s: Int = 0
      while(x > 0) {
        s = f(s, bit(x))
        x -= x & -x
      }
      s
    }

    /**
      * 0 index
      */
    def add(i: Int, a: Int): Unit = {
      assert(i < n)
      var x = i + 1
      while(x <= N) {
        bit(x) = f(bit(x), a)
        x += x & -x
      }
    }

    def sumAll: Int = sum(n)

    /**
      * [l, r)
      */
    def query(l: Int, r: Int)(sub: (Int, Int) => Int): Int = {
      assert(r > l)
      sub(sum(r), sum(l))
    }
  }

  def debug(as: Array[Boolean]): Unit = {
    System.err.println(as.map(x => if(x) "1" else "0").mkString)
  }

  def debug(as: Array[Int]): Unit = {
    System.err.println(as.mkString(" "))
  }

  def debug(as: Array[Long]): Unit = {
    System.err.println(as.mkString(" "))
  }

  def debug(s: String): Unit = {
    System.err.println(s)
  }

  def debug(num: Long): Unit = {
    System.err.println(num)
  }

  class InputReader(val stream: InputStream) {
    private val reader = new BufferedReader(new InputStreamReader(stream), 32768)
    private var tokenizer: StringTokenizer = _

    def next(): String = {
      while (tokenizer == null || !tokenizer.hasMoreTokens)
        tokenizer = new StringTokenizer(reader.readLine)
      tokenizer.nextToken
    }

    def nextInt(): Int = next().toInt
    def nextLong(): Long = next().toLong
    def nextChar(): Char = next().charAt(0)
  }
  val sc = new InputReader(System.in)
  def ni(): Int = sc.nextInt()
  def nl(): Long = sc.nextLong()
  def nc(): Char = sc.nextChar()
  def ns(): String = sc.next()
  def ns(n: Int): Array[Char] = ns().toCharArray
  def na(n: Int, offset: Int = 0): Array[Int] = map(n)(_ => ni() + offset)
  def na2(n: Int, offset: Int = 0): (Array[Int], Array[Int]) = {
    val A1, A2 = Array.ofDim[Int](n)
    REP(n) { i =>
      A1(i) = ni() + offset
      A2(i) = ni() + offset
    }
    (A1, A2)
  }
  def nm(n: Int, m: Int): Array[Array[Int]] = {
    val A = Array.ofDim[Int](n, m)
    REP(n) { i =>
      REP(m) { j =>
        A(i)(j) = ni()
      }
    }
    A
  }
  def nal(n: Int): Array[Long] = map(n)(_ => nl())
  def nm_c(n: Int, m: Int): Array[Array[Char]] = map(n) (_ => ns(m))
  def REP(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = offset
    val N = n + offset
    while(i < N) { f(i); i += 1 }
  }
  def REP_r(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = n - 1 + offset
    while(i >= offset) { f(i); i -= 1 }
  }

  def map[@specialized A: ClassTag](n: Int, offset: Int = 0)(f: Int => A): Array[A] = {
    val res = Array.ofDim[A](n)
    REP(n)(i => res(i) = f(i + offset))
    res
  }


  def sumL(as: Array[Int]): Long = {
    var s = 0L
    REP(as.length)(i => s += as(i))
    s
  }

  def cumSum(as: Array[Int]) = {
    val cum = Array.ofDim[Long](as.length + 1)
    REP(as.length) { i =>
      cum(i + 1) = cum(i) + as(i)
    }
    cum
  }
}

Measured memory_bytes: 91940