#include<bits/stdc++.h>
using namespace std;

#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define lfs <<fixed<<setprecision(10)<<
#define test cout<<"test"<<endl;
#define fi first
#define se second
#define MP make_pair
#define rep(i,n,m) for(ll i = n; i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = n - 1; i >= (ll)(m); i--)
typedef long long ll;
typedef long double ld;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template<typename T>
void chmin(T &a,T b){if(a>b)a=b;}
template<typename T>
void chmax(T &a,T b){if(a<b)a=b;}
void pmod(ll &a,ll b){a=(a+b)%MOD;}
void pmod(ll &a,ll b,ll c){a=(b+c)%MOD;}
void qmod(ll &a,ll b){a=(a*b)%MOD;}
void qmod(ll &a,ll b,ll c){a=(b*c)%MOD;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>
void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>
void debug(vector<vector<T>>v,ll h,ll w){for(ll i=0;i<h;i++)
{cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>v,ll h,ll w){for(ll i=0;i<h;i++)
{for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>
void debug(vector<T>v,ll n){cout<<v[0];
for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>
vector<vector<T>>vec(ll x, ll y, T w){
  vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
template<typename T>
void emp(map<T,ll>&m, T x){m.emplace(x,0).first->second++;}

template<typename T>
struct BIT{
  ll n;
  ll k=1;
  vector<T>data;
  BIT(ll size):n(size){
    data.assign(n,0);
    while(k*2<=n)k*=2;
  }
  void add(ll a,T w){
    for(ll i=a+1;i<=n;i+=i&-i)data[i-1]+=w;
  }
  T sum(ll a){
    T ret = 0;
    for(ll i=a+1;i>0;i-=i&-i)ret+=data[i-1];
    return ret;
  }
  ll search(ll x){
    ll ret=0;    
    for(ll i=k;i>0;i/=2){
      if(ret+i<=n&&data[ret+i-1]<x){
        x-=data[ret+i-1];
        ret+=i;
      }
    }
    return ret;
  }
};

int main(){
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);
  ll res=0,res1=INF,res2=-INF,buf=0;
  bool judge = true;
  ll n;cin>>n;
  vector<char>c(2*n);
  vector<ll>a(2*n);
  rep(i,0,2*n)cin>>c[i]>>a[i];
  auto vb=vec(n+1,n+1,0);
  auto vw=vec(n+1,n+1,0);
  rep(i,0,n+1){
    struct BIT<ll> bit(n+1);
    ll cnt=0;
    rrep(j,2*n,0){
      if(c[j]=='W'){
        if(a[j]<=i)cnt++;
      }
      else{
        vb[a[j]-1][i]=j+bit.sum(a[j])+cnt;
        bit.add(a[j],1);
      }
    }
  }
  rep(i,0,n+1){
    struct BIT<ll> bit(n+1);
    ll cnt=0;
    rrep(j,2*n,0){
      if(c[j]=='B'){
        if(a[j]<=i)cnt++;
      }
      else{
        vw[i][a[j]-1]=j+bit.sum(a[j])+cnt;
        bit.add(a[j],1);
      }
    }
  }
  
  auto dp=vec(2*n+1,n+1,INF);
  dp[0][0]=0;
  rep(i,0,2*n){
    rep(j,max(0LL,i-n),min(i+1,n+1)){
      //cout<<i spa j<<endl;
      if(j!=n){
        chmin(dp[i+1][j+1],dp[i][j]+vb[j][i-j]-i);
      }
      if(i-j!=n){
        chmin(dp[i+1][j],dp[i][j]+vw[j][i-j]-i);
      }
    }
  }
  //debug(dp,2*n,n+1);
  cout<<dp[2*n][n]<<endl;
  return 0;
}

Measured memory_bytes: 94464