#include<bits/stdc++.h>
using namespace std;
int n, ma = INT_MIN, mi = INT_MAX;
int sum = 0;
bool size[1000100] = {0};
int a[1000100], b[1000100];
int main(){
	cin >> n;
	for(int i = 1; i <= n; i++){
		cin >> a[i] >> b[i];
		mi = min(mi, a[i]);
		ma = max(ma, b[i]);
		for(int j = a[i]+1; j <= b[i]; j++){
			size[j] = true;
		}
	}
	for(int i = mi; i <= ma; i++){
		if(size[i] == 1) sum++;
	}
	cout << sum;
	return 0;
}