#include <bits/stdc++.h>

#define maxn 10005
#define mod 1000000007

using namespace std;

int n;

int f[maxn][maxn];

int a[maxn];
char s[maxn][5];

int vis[maxn];

int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n * 2; i++) {
		scanf("%s%d", s[i], &a[i]);
		if (a[i]) ++vis[a[i]];
	}
	f[0][0] = 1;
	int tot = 0;
	for (int i = 1; i <= n * 2; i++) {
		if (vis[a[i]] == 2) {
			for (int j = 0; j <= n; j++) 
				f[i][j] = f[i - 1][j];
			continue;
		}
		if (s[i][0] == 'I') ++tot;
		else --tot;
		for (int j = 0; j <= tot; j++) {
			for (int k = tot - j; k <= tot - j; k++) {
				if (s[i][0] == 'I') {
					if (a[i] == 0) f[i][j] = (j ? f[i - 1][j - 1] : 0);
					else f[i][j] = (k > 0 ? f[i - 1][j] : 0);
				}
				else {
					if (a[i] == 0) f[i][j] = (1ll * f[i - 1][j + 1] * (j + 1) % mod + 1ll * f[i - 1][j] * (k + 1) % mod) % mod;
					else f[i][j] = 1ll * f[i - 1][j + 1] * (j + 1) % mod;
				}
				
			}
		}
	}
	int res = f[n * 2][0];
	int cnt = 0;
	for (int i = 1; i <= n; i++) cnt += (vis[i] == 0);
	while (cnt) {
		res = 1ll * res * cnt % mod;
		--cnt;
	}
	printf("%d\n", res);
//	printf("%d\n", f[n * 2][0][0]);
	return 0;
}