#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
typedef long long ll;
#define int ll
int a[5010], c[5010];
bool b[5010];
int f[5010][5010];
inline void admod(int &a, int b)
{
	a += b;
	if(a >= mod)
		a -= mod;
}
signed main()
{
	int n;
	scanf("%lld", &n);
	int N = 2 * n;
	for(int i = 1; i <= N; i++)
	{
		char ch;
		while((ch = getchar()) != 'I' && ch != 'O');
		b[i] = (ch == 'O');
		scanf("%lld", &a[i]);
		c[a[i]]++;
	}
	int cnt = 0;
	f[0][0] = 1;
	for(int i = 1; i <= N; i++)
	{
		if(a[i] && c[a[i]] == 2)
		{
			for(int j = 0; j <= n; j++)
				f[i][j] = f[i - 1][j];
			continue;
		}
		for(int j = 0; j <= n; j++)
		{
			if(!b[i])
			{
				if(!a[i])
					admod(f[i][j], f[i - 1][j]);
				else if(j)
					admod(f[i][j], f[i - 1][j - 1]);
			}
			else
			{
				if(!a[i])
				{
					admod(f[i][j], f[i - 1][j + 1] * (j + 1) % mod);
					admod(f[i][j], f[i - 1][j] * (cnt - j) % mod);
				}
				else
					admod(f[i][j], f[i - 1][j] * (cnt - j) % mod);
			}
		}
		cnt += (b[i] ? -1 : 1);
	}
	int rem = 0;
	for(int i = 1; i <= n; i++)
		rem += !c[i];
	int ans = f[N][0];
	for(int i = 1; i <= rem; i++)
		ans = ans * i % mod;
	printf("%lld\n", ans);
	return 0;
}