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

int main()
{
	int n, x, sum1 = 0, sum2 = 0;
	cin >> n;
	vector<int> a(n);
	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
	}
	for (int i = 0; i < n; i+=2)
	{
		sum1 += a[i];
	}
	for (int i = 1; i < n; i+=2)
	{
		sum2 += a[i];
	}
	cout << sum1 - sum2;
	//system("pause");
	return 0;
}