#include <bits/stdc++.h>
#define For(i, a, b) for(int i = a; i <= b; i++)
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define sz(x) ((int)x.size())
#define eb emplace_back
#define int LL
using namespace std;
using LL = long long;
using pii = pair<int, int>;

const int MAXN = 5000;
const int MOD = 1'000'000'007;

int dp[MAXN + 10][MAXN + 10];

int32_t main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n; cin >> n;
    vector<int> cnt(n + 1, 0);
    vector<pii> v(n * 2);  // {1/-1, k}
    for(auto &i:v) {
        char ch; cin >> ch;
        i.F = (ch == 'I') - (ch == 'O');
        cin >> i.S;
        cnt[i.S]++;
    }
    int fac = 1;
    {
        vector<pii> swp;
        swp.eb(-1, -1);
        for(auto &i:v) {
            if(cnt[i.S] != 2) swp.eb(i);
        }
        swp.swap(v);
        int cc = 0;
        For(i, 1, n) if(cnt[i] == 0) {
            cc++;
            fac = fac * cc % MOD;
        }
    }
    int m = sz(v) - 1;

    int dif = 0;  // #I - #O
    dp[0][0] = 1;
    For(i, 1, m) {
        // cerr << v[i].F << " " << v[i].S << "\n";
        if(v[i].F > 0 && v[i].S == 0) {
            For(c, 1, m) dp[i][c] = dp[i - 1][c - 1];
        } else if(v[i].F > 0) {
            For(c, 0, m) dp[i][c] = dp[i - 1][c];
        } else if(v[i].S == 0) {
            For(c, 0, m) {
                int t = dif - c;
                if(c > 0) dp[i][c - 1] += dp[i - 1][c] * c;
                if(t > 0) dp[i][c] += dp[i - 1][c] * t;
            }
            For(c, 0, m) dp[i][c] %= MOD;
        } else {
            For(c, 1, m) dp[i][c - 1] = dp[i - 1][c] * c % MOD;
        }
        dif += v[i].F;
    }
    // For(c, 0, m / 2) For(i, 1, m) cout << dp[i][c] << " \n"[i == m];
    cout << dp[m][0] * fac % MOD << "\n";
    return 0;
}