#include "bits/stdc++.h"
#include "atcoder/all"
#include "iomanip"
#include "algorithm"
#include "vector"
#include "math.h"
#include "bitset"
#include "random"
#include "set"
using namespace std;
using namespace atcoder;
#define rep(i, a, b) for(int i = a; i < (int)(b); i++)
#define rrep(i, a, b) for(int i = a; i >= (int)(b); i--)
#define vec vector
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pub push_back
#define pob pop_back
#define prec setprecision
#define ll long long
#define ull unsigned long long
#define maxE *max_element
#define minE *min_element
#define p_queue priority_queue
using Graph = vec<vec<int>>;
using Pi = pair<ll,ll>;
const ll INF = 9E+18;

int main() {
	int N; cin >> N;
	vec<int> L(N),R(N);
	rep(i,0,N) cin >> L[i] >> R[i];
	vec<int> p = {0,1,2,3,4,5,6,7};
	
	int cnt = 0;
	do{
		int lim = -1; bool exist = true;
		rep(i,0,8){
			if(lim > R[p[i]]){
				exist = false;
				break;
			}
			lim = max(lim,L[p[i]]);
		}
		if(exist) cnt++;
		
	}while(next_permutation(all(p)));
	
	cout << cnt << endl;
		
}