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.
/* @nikhil_supertramp */

import java.awt.*;
import java.io.*;
import java.math.*;
import java.util.*;


public class AlmostArithmeticProgression
{
    public static void main(String[] args)throws Exception
    {
        new Solver().solve();
    }
}
class Solver {
    final Helper hp;
    final int MAXN = 1000_006;
    final long MOD = (long) 1e9 + 7;

//javac -d ../../classes
//problem link : https://codeforces.com/contest/978/problem/D

    void solve() throws Exception
    {
        int n = hp.nextInt();
        if(n <= 2)
            hp.println(0);
        else
        {
            int[] arr = hp.getIntArray(n);
            int min  = Integer.MAX_VALUE;
            for(int i = -1; i <= 1; i++)
            {
                //hp.println(i);
                for(int j = -1; j <= 1; j++)
                {
                    int[] ans = new int[n];
                    ans[0] = arr[0] + i;
                    ans[1] = arr[1] + j;
                    int diff = ans[1] - ans[0];
                    for(int p = 2; p < n; p++)
                    {
                        ans[p] = ans[p - 1] + diff;
                    }
                    min = Math.min(min, min(ans, arr));
                    //hp.println(i + " " + j +  "  arrau is : " + Arrays.toString(ans));
                }

            }

            hp.println(min == Integer.MAX_VALUE ? -1 : min);
        }
        hp.flush();
    }

    int min(int[] a, int[] b)
    {
        int count = 0;
        for(int i = 0; i < a.length; i++)
        {
            int dif = Math.abs(a[i] - b[i]);
            if(dif > 1)return Integer.MAX_VALUE;
            count += dif;
        }
        return count;
    }

    Solver() {
        hp = new Helper(MOD, MAXN);
        hp.initIO(System.in, System.out);
    }
}

class Helper {
    final long MOD;
    final int MAXN;
    final Random rnd;

    public Helper(long mod, int maxn) {
        MOD = mod;
        MAXN = maxn;
        rnd = new Random();
    }

    public static int[] sieve;
    public static ArrayList<Integer> primes;

    public void setSieve() {
        primes = new ArrayList<>();
        sieve = new int[MAXN];
        int i, j;
        for (i = 2; i < MAXN; ++i)
            if (sieve[i] == 0) {
                primes.add(i);
                for (j = i; j < MAXN; j += i) {
                    sieve[j] = i;
                }
            }
    }


    public static long[] factorial;

    public void setFactorial() {
        factorial = new long[MAXN];
        factorial[0] = 1;
        for (int i = 1; i < MAXN; ++i) factorial[i] = factorial[i - 1] * i % MOD;
    }

    public long getFactorial(int n) {
        if (factorial == null) setFactorial();
        return factorial[n];
    }

    public long ncr(int n, int r) {
        if (r > n) return 0;
        if (factorial == null) setFactorial();
        long numerator = factorial[n];
        long denominator = factorial[r] * factorial[n - r] % MOD;
        return numerator * pow(denominator, MOD - 2, MOD) % MOD;
    }


    public long[] getLongArray(int size) throws Exception {
        long[] ar = new long[size];
        for (int i = 0; i < size; ++i) ar[i] = nextLong();
        return ar;
    }

    public int[] getIntArray(int size) throws Exception {
        int[] ar = new int[size];
        for (int i = 0; i < size; ++i) ar[i] = nextInt();
        return ar;
	}

    public int[] getIntArray(String s)throws Exception
    {
        s = s.trim().replaceAll("\\s+", " ");
        String[] strs = s.split(" ");
        int[] arr = new int[strs.length];
        for(int i = 0; i < strs.length; i++)
        {
            arr[i] =  Integer.parseInt(strs[i]);
        }
        return arr;
    }

	public long gcd(long a, long b) {
        return b == 0 ? a : gcd(b, a % b);
    }

    public int gcd(int a, int b) {
        return b == 0 ? a : gcd(b, a % b);
    }


    public long max(long[] ar) {
        long ret = ar[0];
        for (long itr : ar) ret = Math.max(ret, itr);
        return ret;
    }

    public int max(int[] ar) {
        int ret = ar[0];
        for (int itr : ar) ret = Math.max(ret, itr);
        return ret;
    }

    public long min(long[] ar) {
        long ret = ar[0];
        for (long itr : ar) ret = Math.min(ret, itr);
        return ret;
    }

    public int min(int[] ar) {
        int ret = ar[0];
        for (int itr : ar) ret = Math.min(ret, itr);
        return ret;
    }


    public long sum(long[] ar) {
        long sum = 0;
        for (long itr : ar) sum += itr;
        return sum;
    }

    public long sum(int[] ar) {
        long sum = 0;
        for (int itr : ar) sum += itr;
        return sum;
    }

    public void shuffle(int[] ar) {
        int r;
        for (int i = 0; i < ar.length; ++i) {
            r = rnd.nextInt(ar.length);
            if (r != i) {
                ar[i] ^= ar[r];
                ar[r] ^= ar[i];
                ar[i] ^= ar[r];
            }
        }
    }

    public void shuffle(long[] ar) {
        int r;
        for (int i = 0; i < ar.length; ++i) {
            r = rnd.nextInt(ar.length);
            if (r != i) {
                ar[i] ^= ar[r];
                ar[r] ^= ar[i];
                ar[i] ^= ar[r];
            }
        }
    }

    public long pow(long base, long exp, long MOD) {
        base %= MOD;
        long ret = 1;
        while (exp > 0) {
            if ((exp & 1) == 1) ret = ret * base % MOD;
            base = base * base % MOD;
            exp >>= 1;
        }
        return ret;
    }


    static byte[] buf = new byte[1000_006];
    static int index, total;
    static InputStream in;
    static BufferedWriter bw;


    public void initIO(InputStream is, OutputStream os) {
        try {
            in = is;
            bw = new BufferedWriter(new OutputStreamWriter(os));
        } catch (Exception e) {
        }
    }

    public void initIO(String inputFile, String outputFile) {
        try {
            in = new FileInputStream(inputFile);
            bw = new BufferedWriter(new OutputStreamWriter(
                    new FileOutputStream(outputFile)));
        } catch (Exception e) {
        }
    }

    private int scan() throws Exception {
        if (index >= total) {
            index = 0;
            total = in.read(buf);
            if (total <= 0)
                return -1;
        }
        return buf[index++];
    }

    public String nextLine() throws Exception {
        int c;
        for (c = scan(); c <= 32; c = scan()) ;
        StringBuilder sb = new StringBuilder();
        for (; c >= 32; c = scan())
            sb.append((char) c);
        return sb.toString();
    }

    public String next() throws Exception {
        int c;
        for (c = scan(); c <= 32; c = scan()) ;
        StringBuilder sb = new StringBuilder();
        for (; c > 32; c = scan())
            sb.append((char) c);
        return sb.toString();
    }

    public int nextInt() throws Exception {
        int c, val = 0;
        for (c = scan(); c <= 32; c = scan()) ;
        boolean neg = c == '-';
        if (c == '-' || c == '+')
            c = scan();
        for (; c >= '0' && c <= '9'; c = scan())
            val = (val << 3) + (val << 1) + (c & 15);
        return neg ? -val : val;
    }

    public long nextLong() throws Exception {
        int c;
        long val = 0;
        for (c = scan(); c <= 32; c = scan()) ;
        boolean neg = c == '-';
        if (c == '-' || c == '+')
            c = scan();
        for (; c >= '0' && c <= '9'; c = scan())
            val = (val << 3) + (val << 1) + (c & 15);
        return neg ? -val : val;
    }

    public void print(Object a) throws Exception {
        bw.write(a.toString());
    }

    public void printsp(Object a) throws Exception {
        print(a);
        print(" ");
    }

    public void println() throws Exception {
        bw.write("\n");
    }

    public void println(Object a) throws Exception {
        print(a);
        println();
    }

    public void flush() throws Exception {
        bw.flush();
    }
}
class Pair implements Comparable<Pair>{
    int x;
    int y;//long z;

    public Pair(int x, int y)
    {
        this.x = x;
        this.y = y;
        //this.z = z;
    }
    @Override
    public int compareTo(Pair p)
    {
        if(p.y == y)
        return x - p.x;
        return p.y - y;
    }
}
