#include <iostream>
#include <vector>

using namespace std;

class my_pair {
public:
	long long nom;
	int right_border;

	my_pair() {}
	my_pair(long long a, long long det) {
		nom = a;
		right_border = det;
	}
};

class my_heap {
public:
	long long one_layer(vector <my_pair> &dot, long long size);

private:
	void sort_heap(vector<my_pair> &dot, long long diff);
	void sift_down(vector<my_pair> &dot, long long number, long long size);
};

long long my_heap::one_layer(vector <my_pair> &dot, long long size) {
	sort_heap(dot, size);

	long long res = 0;
	long long temp = 1;
	my_pair prev = dot[0];

	for (long long i = 1; i < size; i++) {
		if (temp == 1) {
			res += dot[i].nom - prev.nom;
		}

		if (dot[i].right_border = 1) {
			temp--;
		}
		if (dot[i].right_border = 0) {
			temp++;
		}

		prev = dot[i];
	}
	return res;
}

void my_heap::sift_down(vector<my_pair> &dot, long long number, long long size) {
	long long left = 2 * number + 1;
	long long right = 2 * number + 2;
	long long max = number;

	if (right < size && dot[right].nom > dot[max].nom) {
		max = right;
	}
	if (left < size && dot[left].nom > dot[max].nom) {
		max = left;
	}

	if (max != number) {
		swap(dot[max], dot[number]);
		sift_down(dot, max, size);
	}
}

void my_heap::sort_heap(vector<my_pair> &dot, long long diff) {
    for (long long i = diff / 2 - 1; i >= 0; i--) {
		sift_down(dot, i, diff);
	}

	for (long long i = diff - 1; i >= 0; i--) {
		swap(dot[0], dot[i]);
		sift_down(dot, 0, i);
	}
}

int main() {
	long long n = 0;
	cin >> n;

	my_heap solvation;
	vector <my_pair> array(2 * n);

	for (long long i = 0; i < 2 * n; i++) {
		int right_border = i % 2;

		int nom = 0;
		cin >> nom;
		array[i] = my_pair(nom, right_border);
	}

    cout << solvation.one_layer(array, 2 * n);
	return 0;
}