#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;
struct cmp{
	bool operator()(const pair<int, int>& a, const pair<int, int>& b){
		return a.first < b.first;
	}
};
int main(){
	int n;
	cin >> n;
	vector<pair<int, int>> dp(n);
	//ÊäÈë 
	for(int i = 0; i < n; i++){
		cin >> dp[i].first >> dp[i].second;
	} 
	//°´ÕÕdp.firstÅÅÐò 
	sort(dp.begin(), dp.end(), cmp());
	vector<pair<int, int>> merge;
	for(auto [l, r] : dp){
		if (merged.empty() || merged.back().second < l)
        	merged.push_back({l,r});
    	else
        	merged.back().second = max(merged.back().second, r);
	}
	int sum = 0;
	for(auto [l, r] : merge){
		sum += r - l;
	}
	cout << sum << endl;
	return 0;
}