#include <iostream>
#include <vector>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    vector<int>L(N), R(N);
    for (int i = 0;i < N;i++) {
        cin >> L[i] >> R[i];
    }
    if(N > 2501){
    	cout<<-1;
    	return 0;
    }
    //愚直
    int ans = 0;
    for (int i = 0;i < N;i++) {
        for (int j = i + 1;i < N;i++) {
        	if(L[i] < L[j] < R[j] < R[i])ans++;
    	}
    }
    cout << ans;
    return 0;
}