#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,m,x[3005],o[3005];
int a[3005],b[3005],cc[3005][3005];
int dp[2][3005];
const int p=1e9+7;
signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	int i,j,k,r,id;
	cin>>n;
	for(i=1;i<=n;i++)cin>>o[i]>>x[i];
	for(i=1;i<=n;i++)
	{
		for(j=1;j<=n;j++)
		{
			if(x[j]<=i)
			{
				if(o[j]==1)a[i]++;
				else b[i]++;
			}
		}
	}
	for(i=0;i<=n;i++)
	{
		cc[i][0]=cc[i][i]=1;
		for(j=1;j<i;j++)cc[i][j]=(cc[i-1][j-1]+cc[i-1][j])%p;
	}
	dp[0][0]=1;
	id=0;
	for(i=1;i<=n;i++)
	{
		for(j=0;j<=i;j++)dp[id^1][j]=0;
		for(j=0;j<i;j++)
		{
			dp[id^1][j+1+b[i]-b[i-1]]=(dp[id^1][j+1+b[i]-b[i-1]]+dp[id][j]*(a[i]-(j-b[i-1]))%p*cc[i-(j+1)][b[i]-b[i-1]])%p;
			dp[id^1][j+b[i]-b[i-1]]=(dp[id^1][j+b[i]-b[i-1]]+dp[id][j]*cc[i-j][b[i]-b[i-1]])%p;
		}
		id^=1;
	}
	cout<<dp[id][n]<<"\n";
    return 0;
}
/*






*/