#include <bits/stdc++.h>
#define ll long long

using namespace std;

const int maxN = 4005;

int pos[2][maxN], f[maxN][maxN], cost1[maxN][maxN], cost2[maxN][maxN];

int main()
{
    ios_base::sync_with_stdio(false); cin.tie(); cout.tie();
    int n;
    cin >> n;

    for(int i = 1; i <= n * 2; ++i){
        char c;
        int x;
        cin >> c >> x;

        if(c == 'B') pos[0][x] = i;
        else pos[1][x] = i;
    }

    for(int i = 1; i <= n; ++i){
        for(int j = 1; j <= n; ++j){
            cost1[i][j] = cost1[i][j-1];
            cost2[j][i] = cost2[j][i-1];
            if(pos[0][i] < pos[1][j])
                ++cost1[i][j];
            else
                ++cost2[j][i];
        }
    }

    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= n; ++j)
            f[i][j] = min(f[i-1][j] + cost1[i][j], f[i][j-1] + cost2[j][i]);

    int res = 0;
    for(int i = 1; i <= n; ++i)
        for(int j = i + 1; j <= n; ++j){
            if(pos[0][i] > pos[0][j]) ++res;
            if(pos[1][i] > pos[1][j]) ++res;
        }

    cout << res + f[n][n];
}
