#include<cstdio>
#include <iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<int, int> Pr;

ll N, X[100010];
int main()
{
	cin >> N;
	for (int i = 0; i < N; i++) {
		cin >> X[i];
	}
	sort(X,X+N);
	int mi = 100000000;
	for (int i = 0; i < N-1; i++) {
		if (X[i+1] != X[i] && mi > X[i + 1] - X[i]) {
			mi = X[i + 1] - X[i];
		}
	}
	if (mi != 100000000)
		cout << mi << endl;
	else
		cout << -1 << endl;
	return 0;
}