ll l[8],r[8];
ll f(ll b,ll d){
	if(!b){
		return 1;
	}else{
		ll z=0;
		rep(i,8){
			if(b&1<<i&&d<=r[i]){
				z+=f(b^1<<i,max(d,l[i]));
			}
		}
		return z;
	}
}
{
	ll@n;
	rd((l,r)(n));
	wt(f((1<<n)-1,0));
}