#include<iostream>
#include<algorithm>
#include <vector>
#include<cmath>
#include<iomanip>
using namespace std;
typedef long long int lont;
int main() {
	int N, K;
	cin >> N >> K;
	vector<int>vec(N);
	for (int ia = 0; ia < N; ia++) {
		cin >> vec.at(ia);
	}
	sort(vec.begin(), vec.end());
	cout << (vec.at(N - 1) - vec.at(0)) / 2<<endl;
}