#pragma GCC optimizer("Ofast")
#pragma GCC target("avx2")
#include <bits/stdc++.h>
//#define int long long 
#define ld long double
#define ull unsigned long long 
#define fr first
#define fi first
#define sc second
#define se second
#define all(x) x.begin(), x.end()
#define pii pair<int,int>
using namespace std;

#ifndef fireball
#define tofu ios::sync_with_stdio(0); cin.tie(0);
#else
#define tofu freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout);
#endif 

void db() {cout << '\n';}
template <typename T, typename ...U> void db(T a, U ...b) {cout << a << ' ', db(b...);}

const int mod = 1e9 + 7;

signed main(){
    tofu;
    int n; cin >> n;
    vector<pair<char, int> > a(2 * n);
    int cnt[n + 1] = {};
    for(int i = 0; i < 2 * n; ++i){
        cin >> a[i].fr >> a[i].sc;
        cnt[a[i].sc]++;
    }
    vector<pair<char,int> > v;
    int unknown = 0, input = 0, frac = 0;
    for(auto i : a){
        if(i.sc == 0 or cnt[i.sc] < 2) v.push_back(i);
        if(i.fr == 'O' and i.sc == 0) unknown++;
    }
    for(int i = 1; i <= n; ++i) if(cnt[i] == 0) frac++;
    n = (int)v.size() / 2;

    int dp[2][n + 1], now = 0;
    for(int i = 0; i <= n; ++i) dp[0][i] = dp[1][i] = 0;
    dp[0][0] = 1;

    for(auto i : v){
        if(i.fr == 'I' and i.sc > 0){
            for(int j = 0; j + 1 <= unknown; ++j){
                dp[now ^ 1][j + 1] = dp[now][j] % mod;

            }
            now ^= 1;
            input++;
        }

        if(i.fr == 'I' and i.sc == 0){
            for(int j = 0; j <= unknown; ++j){
                dp[now ^ 1][j] += dp[now][j];
                if(j + 1 <= unknown) dp[now ^ 1][j + 1] += dp[now][j];
            }
            now ^= 1;
            for(int j = 0; j <= n; ++j) dp[now][j] %= mod;
            input++;
        }

        if(i.fr == 'O' and i.sc > 0){
            for(int j = 0; j <= unknown; ++j){
                dp[now ^ 1][j] += dp[now][j] * (input - j);
                dp[now ^ 1][j] %= mod;
            }
            now ^= 1;
            input--;
        }

        if(i.fr == 'O' and i.sc == 0){
            input--;
            for(int j = 1; j <= unknown; ++j){
                dp[now ^ 1][j - 1] += dp[now][j] * j;
                dp[now ^ 1][j - 1] %= mod;
            }
            unknown--;
            now ^= 1;
        }

        for(int j = 0; j <= n; ++j){
            //cout << dp[now][j] << ' ';
            dp[now ^ 1][j] = 0;
        }
        //db(unknown);
    }

    int ans = dp[now][0];
    for(int i = 1; i <= frac; ++i) ans = (ans * i) % mod;
    db(ans);
}