#include <bits/stdc++.h>
#define x first
#define y second
#define pb push_back
#define all(v) v.begin(),v.end()
using namespace std;
typedef pair<int,int> pi;
typedef long long ll;
int n;
pair <char,int> ta[10005],a[10005];
ll d[2][5005];
ll mod = 1e9+7;
int c[5005];
int s[4][5005]; // I,nI,O,nO

int main() {
    ios_base::sync_with_stdio(false); cin.tie(0);
    cin >> n;
    for(int i = 1;i <= 2*n;i++) {
        cin >> ta[i].x >> ta[i].y;
        c[ta[i].y] += 1;
    }
    int m = 0;
    for(int i = 1;i <= 2*n;i++) {
        if(ta[i].y&&c[ta[i].y] == 2) continue;
        a[++m] = ta[i];
    }
    n = m/2;
    d[0][0] = 1;
    for(int i = 1;i <= n*2;i++) {
        for(int j = 0;j < 4;j++) s[j][i] = s[j][i-1];
        int op = 0;
        if(a[i].x == 'O') op += 2;
        if(!a[i].y) op += 1;
        s[op][i]++;
    }
    int nam = n-s[0][n*2]-s[2][n*2];
    for(int i = 1;i <= n*2;i++) {
        char op = a[i].x;
        int val = a[i].y,I,nI;
        //cout << op << ' ' << val << '\n';
        int vs = s[1][i];
        for(int j = 0;j <= vs;j++) {
            I = s[0][i-1]-s[3][i-1]+j;
            nI = s[1][i-1]-s[2][i-1]-j+1;
            
            if(op == 'I') {
                d[i%2][j] = d[(i-1)%2][j];
                if(!val) d[i%2][j] = 1LL*d[(i-1)%2][j]%mod;
            }
            else if(!val) {
                d[i%2][j] = (1LL*d[(i-1)%2][j]*I%mod + 1LL*d[(i-1)%2][j-1]*nI%mod*(nam+1-j)%mod)%mod;
            }
            else {
                d[i%2][j] = 1LL*d[(i-1)%2][j]*(nI-1)%mod;
            }
            //cout << d[i%2][j] << ' ';
            //cout << I << ' ' << nI << " : " << d[i%2][j] << '\n';
        }
        //cout << '\n';
        for(int j = 0;j <= n;j++) {
            d[(i-1)%2][j] = 0;
        }
        //if(op == 'I'&&!val) nam--;
    }
    ll ans = 0;
    for(int i = 0;i <= n;i++) ans = (ans+d[0][i])%mod;
    cout << ans;
    
}