Polycarp likes arithmetic progressions. A sequence [a_1, a_2, ..., a_n] is called an arithmetic progression if for each i (1 ≤ i < n) the value a_{i+1} - a_i is the same. For example, the sequences [42], [5, 5, 5], [2, 11, 20, 29] and [3, 2, 1, 0] are arithmetic progressions, but [1, 0, 1], [1, 3, 9] and [2, 3, 1] are not.

It follows from the definition that any sequence of length one or two is an arithmetic progression.

Polycarp found some sequence of positive integers [b_1, b_2, ..., b_n]. He agrees to change each element by at most one. In the other words, for each element there are exactly three options: an element can be decreased by 1, an element can be increased by 1, an element can be left unchanged.

Determine a minimum possible number of elements in b which can be changed (by exactly one), so that the sequence b becomes an arithmetic progression, or report that it is impossible.

It is possible that the resulting sequence contains element equals 0.

Input

The first line contains a single integer n (1 ≤ n ≤ 100 000) — the number of elements in b.

The second line contains a sequence b_1, b_2, ..., b_n (1 ≤ b_i ≤ 10^{9}).

Output

If it is impossible to make an arithmetic progression with described operations, print -1. In the other case, print non-negative integer — the minimum number of elements to change to make the given sequence becomes an arithmetic progression. The only allowed operation is to add/to subtract one from an element (can't use operation twice to the same position).

Examples

Input

4
24 21 14 10


Output

3


Input

2
500 500


Output

0


Input

3
14 5 1


Output

-1


Input

5
1 3 6 9 12


Output

1

Note

In the first example Polycarp should increase the first number on 1, decrease the second number on 1, increase the third number on 1, and the fourth number should left unchanged. So, after Polycarp changed three elements by one, his sequence became equals to [25, 20, 15, 10], which is an arithmetic progression.

In the second example Polycarp should not change anything, because his sequence is an arithmetic progression.

In the third example it is impossible to make an arithmetic progression.

In the fourth example Polycarp should change only the first element, he should decrease it on one. After that his sequence will looks like [0, 3, 6, 9, 12], which is an arithmetic progression.
import java.io.*;
import java.math.*;
import java.util.*;

public class test {
	public static void main(String[] args) {
//		int test = fs.nextInt();
		int test = 1;
		for (int cases = 0; cases < test; cases++) {
			int n = fs.nextInt();
			int arr[] = new int[n];
			for (int i = 0; i < n; i++) {
				arr[i] = fs.nextInt();
			}
			if (n > 2) {
				int x = 0;
				int y = 0;
				int d = 0;
				boolean rs = false;
				int count = 0;
				int mincount = Integer.MAX_VALUE;
				int s = arr[0];
				int e = arr[1];
				for (int i = 1; i <= 9; i++) {
					count = 0;
					if (i == 1) {
						x = s;
						y = e;
					} else if (i == 2) {
						x = s;
						y = e + 1;
						count += 1;
					} else if (i == 3) {
						x = s;
						y = e - 1;
						count += 1;
					} else if (i == 4) {
						x = s + 1;
						y = e;
						count += 1;
					} else if (i == 5) {
						x = s + 1;
						y = e + 1;
						count += 2;
					} else if (i == 6) {
						x = s + 1;
						y = e - 1;
						count += 2;
					} else if (i == 7) {
						x = s - 1;
						y = e;
						count += 1;
					} else if (i == 8) {
						x = s - 1;
						y = e + 1;
						count += 2;
					} else if (i == 9) {
						x = s - 1;
						y = e - 1;
						count += 2;
					}
					rs = true;
					d = y - x;
					int ar[] = Arrays.copyOf(arr, n);
					ar[0] = x;
					ar[1] = y;

					for (int k = 2; k < n; k++) {
						int a = ar[k] - ar[k - 1] - 1;
						int b = ar[k] - ar[k - 1];
						int c = ar[k] - ar[k - 1] + 1;
						if (d == a || d == b || d == c) {
							if (d == a || d == c) {
								count += 1;
							}
							if (d == a) {
								ar[k] -= 1;
							} else if (d == c) {
								ar[k] += 1;
							}
							continue;
						} else {
							rs = false;
							break;
						}
					}
					if (rs) {
//						System.out.println(Arrays.toString(ar));
//						System.out.println(count + " " + mincount);
						mincount = Integer.min(count, mincount);
//						System.out.println(count + " " + mincount);

					}
				}
				if (mincount != Integer.MAX_VALUE) {
					op.print(mincount);
				} else {
					op.print(-1);
				}
			} else {
				op.print(0);
			}
			op.flush();
		}

	}

	static void sieve() {
		boolean prime[] = new boolean[101];
		Arrays.fill(prime, true);
		prime[1] = false;
		for (int i = 2; i * i <= prime.length - 1; i++) {
			for (int j = i * i; j <= prime.length - 1; j += i) {
				prime[j] = false;
			}
		}
	}

	static void printArray(int ar[]) {
		Arrays.toString(ar);
	}

	static long expmodulo(long a, long b, long c) {
		long x = 1;
		long y = a;
		while (b > 0) {
			if (b % 2 == 1) {
				x = (x * y) % c;
			}
			y = (y * y) % c; // squaring the base
			b /= 2;
		}
		return (long) x % c;
	}

	static int modInverse(int a, int m) {
		int m0 = m;
		int y = 0, x = 1;

		if (m == 1)
			return 0;

		while (a > 1) {
			int q = a / m;
			int t = m;
			m = a % m;
			a = t;
			t = y;
			y = x - q * y;
			x = t;
		}
		if (x < 0)
			x += m0;
		return x;
	}

	static int countBits(int number) {
		return (int) (Math.log(number) / Math.log(2) + 1);
	}

	static int countDifferentBits(int a, int b) {
		int count = 0;
		for (int i = 0; i < 32; i++) {
			if (((a >> i) & 1) != ((b >> i) & 1)) {
				++count;
			}
		}
		return count;
	}

	static int gcd(int a, int b) {
		if (b == 0)
			return a;
		return gcd(b, a % b);
	}

	static void sortMyMapusingValues(HashMap<String, Integer> hm) {

		List<Map.Entry<String, Integer>> capitalList = new LinkedList<>(hm.entrySet());

		Collections.sort(capitalList, new Comparator<Map.Entry<String, Integer>>() {
			public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
				return (o1.getValue()).compareTo(o2.getValue());
			}
		});
		HashMap<String, Integer> result = new HashMap<>();
		for (Map.Entry<String, Integer> entry : capitalList) {
			result.put(entry.getKey(), entry.getValue());
		}
	}

	static boolean ispowerof2(long num) {
		if ((num & (num - 1)) == 0)
			return true;
		return false;
	}

	static void primeFactors(int n) {
		while (n % 2 == 0) {
			System.out.print(2 + " ");
			n /= 2;
		}
		for (int i = 3; i <= Math.sqrt(n); i += 2) {
			while (n % i == 0) {
				System.out.print(i + " ");
				n /= i;
			}
		}
		if (n > 2)
			System.out.print(n);
	}

	static boolean isPrime(long n) {
		// Corner cases
		if (n <= 1)
			return false;
		if (n <= 3)
			return true;
		if (n % 2 == 0 || n % 3 == 0)
			return false;

		long sq = (long) Math.sqrt(n);
		for (int i = 5; i <= sq; i = i + 6)
			if (n % i == 0 || n % (i + 2) == 0)
				return false;

		return true;
	}

	static class Graph {
		HashMap<Integer, LinkedList<Integer>> hm = new HashMap<Integer, LinkedList<Integer>>();

		private void addVertex(int vertex) {
			hm.put(vertex, new LinkedList<>());
		}

		private void addEdge(int source, int dest, boolean bi) {
			if (!hm.containsKey(source))
				addVertex(source);
			if (!hm.containsKey(dest))
				addVertex(dest);
			hm.get(source).add(dest);
			if (bi) {
				hm.get(dest).add(source);
			}
		}

		private boolean uniCycle(int i, HashSet<Integer> visited, int parent) {
			visited.add(i);
			LinkedList<Integer> list = hm.get(i);
			Iterator<Integer> it = list.iterator();
			while (it.hasNext()) {
				Integer integer = (Integer) it.next();
				if (!visited.contains(integer)) {
					if (uniCycle(integer, visited, i))
						return true;
				} else if (integer != parent) {
					return true;
				}
			}
			return false;
		}

		private boolean uniCyclic() {
			HashSet<Integer> visited = new HashSet<Integer>();
			Set<Integer> set = hm.keySet();
			for (Integer integer : set) {
				if (!visited.contains(integer)) {
					if (uniCycle(integer, visited, -1)) {
						return true;
					}
				}
			}
			return false;
		}

		private boolean isbiCycle(int i, HashSet<Integer> visited, HashSet<Integer> countered) {
			if (countered.contains(i))
				return true;
			if (visited.contains(i))
				return false;
			visited.add(i);
			countered.add(i);
			LinkedList<Integer> list = hm.get(i);
			Iterator<Integer> it = list.iterator();
			while (it.hasNext()) {
				Integer integer = (Integer) it.next();
				if (isbiCycle(integer, visited, countered)) {
					return true;
				}
			}
			countered.remove(i);
			return false;
		}

		private boolean isbiCyclic() {
			HashSet<Integer> visited = new HashSet<Integer>();
			HashSet<Integer> countered = new HashSet<Integer>();
			Set<Integer> set = hm.keySet();
			for (Integer integer : set) {
				if (isbiCycle(integer, visited, countered)) {
					return true;
				}
			}
			return false;
		}
	}

	static class Node {
		Node left, right;
		int data;

		public Node(int data) {
			this.data = data;
		}

		public void insert(int val) {
			if (val <= data) {
				if (left == null) {
					left = new Node(val);
				} else {
					left.insert(val);
				}
			} else {
				if (right == null) {
					right = new Node(val);
				} else {
					right.insert(val);
				}
			}
		}

		public boolean contains(int val) {
			if (data == val) {
				return true;
			} else if (val < data) {
				if (left == null) {
					return false;
				} else {
					return left.contains(val);
				}
			} else {
				if (right == null) {
					return false;
				} else {
					return right.contains(val);
				}
			}
		}

		public void inorder() {
			if (left != null) {
				left.inorder();
			}
			System.out.print(data + " ");
			if (right != null) {
				right.inorder();
			}
		}

		public int maxDepth() {
			if (left == null)
				return 0;
			if (right == null)
				return 0;
			else {
				int ll = left.maxDepth();
				int rr = right.maxDepth();
				if (ll > rr)
					return (ll + 1);
				else
					return (rr + 1);
			}
		}

		public int countNodes() {
			if (left == null)
				return 1;
			if (right == null)
				return 1;
			else {
				return left.countNodes() + right.countNodes() + 1;
			}
		}

		public void preorder() {
			System.out.print(data + " ");
			if (left != null) {
				left.inorder();
			}

			if (right != null) {
				right.inorder();
			}

		}

		public void postorder() {
			if (left != null) {
				left.inorder();
			}

			if (right != null) {
				right.inorder();
			}
			System.out.print(data + " ");

		}

		public void levelorder(Node node) {
			LinkedList<Node> ll = new LinkedList<Node>();
			ll.add(node);
			getorder(ll);

		}

		public void getorder(LinkedList<Node> ll) {
			while (!ll.isEmpty()) {
				Node node = ll.poll();
				System.out.print(node.data + " ");
				if (node.left != null)
					ll.add(node.left);
				if (node.right != null)
					ll.add(node.right);
			}
		}
	}

	static class FastReader {
		BufferedReader br;
		StringTokenizer st;

		public FastReader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
	}

	static class Pair {
		int first, second;

		public Pair(int first, int second) {
			this.first = first;
			this.second = second;
		}

	}

	static class Pair2 {
		int first;
		Pair second;

		public Pair2(int first, Pair second) {
			this.first = first;
			this.second = second;
		}

	}

	static class LongPair {
		long first, second;

		public LongPair(long first, long second) {
			this.first = first;
			this.second = second;
		}

	}

	static class OutputWriter {
		private final PrintWriter writer;

		public OutputWriter(OutputStream outputStream) {
			writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
		}

		public OutputWriter(Writer writer) {
			this.writer = new PrintWriter(writer);
		}

		public void print(Object... objects) {
			for (int i = 0; i < objects.length; i++) {
				if (i != 0)
					writer.print(' ');
				writer.print(objects[i]);
			}
		}

		public void printLine(Object... objects) {
			print(objects);
			writer.println();
		}

		public void close() {
			writer.close();
		}

		public void flush() {
			writer.flush();
		}

	}

	private static final Scanner sc = new Scanner(System.in);
	private static final FastReader fs = new FastReader();
	private static final OutputWriter op = new OutputWriter(System.out);

	static int[] getintarray(int n) {
		int ar[] = new int[n];
		for (int i = 0; i < n; i++) {
			ar[i] = fs.nextInt();
		}
		return ar;
	}

	static long[] getlongarray(int n) {
		long ar[] = new long[n];
		for (int i = 0; i < n; i++) {
			ar[i] = fs.nextLong();
		}
		return ar;
	}

	static int[][] get2darray(int n, int m) {
		int ar[][] = new int[n][m];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				ar[i][j] = fs.nextInt();
			}
		}
		return ar;
	}

	static Pair[] getpairarray(int n) {
		Pair ar[] = new Pair[n];
		for (int i = 0; i < n; i++) {
			ar[i] = new Pair(fs.nextInt(), fs.nextInt());
		}
		return ar;
	}

	static void printarray(int ar[]) {
		for (int i : ar) {
			op.print(i + " ");
		}
		op.flush();
	}

	static int fact(int n) {
		int fact = 1;
		for (int i = 2; i <= n; i++) {
			fact *= i;
		}
		return fact;
	}

//	

	// function to find largest prime factor

}
