#include<bits/stdc++.h>
#define int long long
#define matsuri pair<int,int>
const int iris = 1e9+7;
//const int iris = 998244353;
using namespace std;

int dp[10001][5001];
char owo[10001];
int arr[10001], cnt[10001], sf[10001], pr[10001], prI[10001], prO[10001];

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    
    int n;
    cin>>n;
    for(int i=1;i<=n*2;i++)
    {
    	cin>>owo[i]>>arr[i];
    	cnt[arr[i]]++;
    	if(arr[i]==0)
    	{
    		if(owo[i]=='I')
    			pr[i]=1;
    		else
    			sf[i]=1;
		}
		pr[i]+=pr[i-1];
	}
	int ooo=0;
	for(int i=1;i<=n;i++)
		if(cnt[i]==0)
			ooo++;
	for(int i=1;i<=n*2;i++)
	{
		if(owo[i]=='I' && !(arr[i] && cnt[arr[i]]==2))
			prI[i]=1;
		if(owo[i]=='O' && !(arr[i] && cnt[arr[i]]==2))
			prO[i]=1;
		prO[i]+=prO[i-1];
		prI[i]+=prI[i-1];
	}
	for(int i=n*2-1;i>=0;i--)
		sf[i]+=sf[i+1];
	dp[0][0]=1;
    for(int i=1;i<=n*2;i++)
    {
    	if((arr[i] && cnt[arr[i]]==2) || (owo[i]=='I' && arr[i]!=0))
    	{
    		for(int j=0;j<=n;j++)
    			dp[i][j]=dp[i-1][j];
		}
		else if(owo[i]=='I')
		{
    		for(int j=1;j<=n;j++)
    			dp[i][j]=dp[i-1][j-1];
		}
		else if(arr[i])
		{
			for(int j=0;j<n;j++)
				dp[i][j]=dp[i-1][j+1]*(j+1)%iris;
			//cout<<'-'<<i<<' '<<'\n';
		}
		else
		{
			for(int j=0;j<=n;j++)
			{
				// prI[i]-prO[i-1]=x+j
				int sp=prI[i]-prO[i-1]-j;
				if(j)
				{
					dp[i][j-1]+=dp[i-1][j]*j;
					dp[i][j-1]%=iris;
				}
				dp[i][j]+=dp[i-1][j]*sp;
				dp[i][j]%=iris;
			}
		}
	}
	cout<<dp[n*2][0]<<'\n';

    return 0;
}