#include<iostream>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
const ll mod=1e9+7 ;


ll dp[20][1<<20];
int main(){
    int n;
    cin>>n;
    int all = 1<<n;
    dp[0][0]=1;
    rep(i,n){
        int x, y;
        cin>>x>>y;
        if(x){
            rep(j,all)REP(k,y-1,n){
                if(j & (1<<k))continue;
                dp[i+1][j|(1<<k)]+=dp[i][j];
                if(dp[i+1][j|(1<<k)]>=mod)dp[i+1][j|(1<<k)]-=mod;
            }
        }
        else {
            rep(j,all)rep(k,y){
                if(j & (1<<k))continue;
                dp[i+1][j|(1<<k)]+=dp[i][j];
                if(dp[i+1][j|(1<<k)]>=mod)dp[i+1][j|(1<<k)]-=mod;
            }
        }
    }
    cout<<dp[n][all-1]<<endl;
    return 0;
}