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

struct Cpoint {
	int point;
	char BeginOrEnd;
};

template <typename Iterator>
void SiftDown(Iterator i, Iterator begin, Iterator end)
{
	Iterator left;
	Iterator right;
	if (2 * distance(begin, i) + 1 < distance(begin, end)) {
		left = i + distance(begin, i) + 1;
	}
	else {
		left = end;
	};
	if (2 * distance(begin, i) + 1 < distance(begin, end)) {
		right = i + distance(begin, i) + 2;
	}
	else {
		right = end;
	};
	Iterator largest = i;
	if (left < end && (*left).point > (*i).point)
		largest = left;
	if (right < end && (*right).point > (*largest).point)
		largest = right;
	if (largest != i) {
		swap(*i, *largest);
		SiftDown(largest, begin, end);
	}
};

template <typename Iterator>
void BuildHeap(Iterator begin, Iterator end)
{
	Iterator i = end - distance(begin, end) / 2 - 1;
	while (i >= begin) {
		SiftDown(i, begin, end);
		if (i == begin) {
			break;
		};
		i--;
	}
};

template <typename iterator>
void HeapSort(iterator begin, iterator end) {
	int heapSize = distance(begin, end);
	BuildHeap(begin, end - 1);
	while (heapSize > 1) {
		heapSize--;
		swap(*begin, *(end - 1));
		end--;
		SiftDown(begin, begin, end);
	}
}

int main()
{
	int n = 0;
	cin >> n;
	vector <Cpoint> line;
	for (int i = 0; i < n; i++) {
		Cpoint element;
		cin >> element.point;
		element.BeginOrEnd = 'B';
		line.push_back(element);
		cin >> element.point;
		element.BeginOrEnd = 'E';
		line.push_back(element);
	};
	HeapSort(line.begin(), line.end());
	int sum = 0;
	int stapleBalance = 1;
	int test = 0;
	for (int i = 1; i < 2 * n; i++) {
		if (line[i].BeginOrEnd == 'B') {
			stapleBalance++;
		}
		else {
			stapleBalance--;
		};
		if (test == 0) {
			sum = sum + line[i].point - line[i - 1].point;
		};
		test = 0;
		if (stapleBalance == 0) {
			test = 1;
		};
	};
	cout << sum;
    //hhh
	return 0;
}