static void Main()
{
Sc sc = new Sc();
int n = sc.I;
Bit bit = new Bit(n * 2);
int[] b = new int[n + 1], w = new int[n + 1];
string[] a = new string[n * 2];
int[] r = new int[n * 2];
for (int i = 0; i < n * 2; i++)
{
a[i] = sc.S;
r[i] = int.Parse((a[i].Split())[1]);
if (a[i][0] == 'B')
{
b[r[i]] = i;
}
else
{
w[r[i]] = i;
}
}
long[,,] dp = new long[n + 1, n + 1, 2];
for (int i = 0; i <= n; i++)
{
bit = new Bit(n * 2);
if (i != 0)
{
for (int j = 1; j < i; j++)
{
bit.Ud(b[j] + 1, 1);
}
dp[i, 0, 0] = dp[i - 1, 0, 0] + b[i] - bit.Get(b[i] + 1);
bit.Ud(b[i] + 1, 1);
}
for (int j = 1; j <= n; j++)
{
dp[i, j, 0] = dp[i, j - 1, 0] + w[j] - bit.Get(w[j] + 1);
if (i != 0)
{
dp[i, j, 0] = Math.Min(dp[i, j, 0], dp[i - 1, j, 0] + b[i] - dp[i - 1, j, 1]);
}
if (j != 0)
{
bit.Ud(w[j] + 1, 1);
}
if (i != n)
{
dp[i, j, 1] = bit.Get(b[i + 1] + 1);
}
}
bit.Clear();
}
Console.WriteLine("{0}", dp[n, n, 0]);
}
