Little penguin Polo has an n × m matrix, consisting of integers. Let's index the matrix rows from 1 to n from top to bottom and let's index the columns from 1 to m from left to right. Let's represent the matrix element on the intersection of row i and column j as aij.

In one move the penguin can add or subtract number d from some matrix element. Find the minimum number of moves needed to make all matrix elements equal. If the described plan is impossible to carry out, say so.

Input

The first line contains three integers n, m and d (1 ≤ n, m ≤ 100, 1 ≤ d ≤ 104) — the matrix sizes and the d parameter. Next n lines contain the matrix: the j-th integer in the i-th row is the matrix element aij (1 ≤ aij ≤ 104).

Output

In a single line print a single integer — the minimum number of moves the penguin needs to make all matrix elements equal. If that is impossible, print "-1" (without the quotes).

Examples

Input

2 2 2
2 4
6 8


Output

4


Input

1 2 7
6 7


Output

-1
import java.io.InputStreamReader;
import java.io.IOException;
import java.awt.List;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Dictionary;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;

import javax.print.attribute.DocAttributeSet;
import javax.print.attribute.HashDocAttributeSet;

import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskA solver = new TaskA();
		solver.solve(1, in, out);
		out.close();
	}
}

class TaskA {
	 public void solve(int testNumber, InputReader in, PrintWriter out) {
		int n = in.nextInt() * in.nextInt();
		int d = in.nextInt();
		int[] g = in.nextIntegerArray(n);
		int mod = g[0] % d;
		for(int i = 1; i < n; i++){
			if(g[i] % d != mod){
				out.println(-1);
				return;
			}
		}
		Arrays.sort(g);
		long value = g[n>>1];
		long res = 0;
		for(int i = 0; i < n; i++)
			res += Math.abs(g[i] - value);
		out.println(res/d);
  }
	 
}
  
  
         //||||||| comparable pair ||||||||
 class pair implements Comparable<pair>{
	 public long first,second;
	 public pair(){
		 first = second = 0;
	 }
	@Override
	public int compareTo(pair arg0) {
		if(this.first > arg0.first)
			return 1;
		else if(this.first < arg0.first)
			return -1;
		else if(this.second > arg0.second)
			return 1;
		else if(this.second < arg0.second)
		     return -1;
		return 0;
	}
 }

 
   // ||||||| INPUT READER ||||||||
class InputReader {
    public BufferedReader reader;
    public StringTokenizer tokenizer;

    public InputReader(InputStream stream) {
        reader = new BufferedReader(new InputStreamReader(stream));
        tokenizer = null;
    }

    public String next() {
        while (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }

    public Integer nextInt() {
        return Integer.parseInt(next());
    }
    
    public Long nextLong() {
    	return Long.parseLong(next());
    }
    
    public Double nextDouble() {
    	return Double.parseDouble(next());
    }
    
    public Float nextFloat() {
    	return Float.parseFloat(next());
    }
    
    public BigInteger nextBigInteger() {
    	return new BigInteger(next());
    }
    
    public String nextLine() {
    	try {
			return reader.readLine();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return null;
		}
    	
    }
    
    public int[] nextIntegerArray(int n) {
    	int[] a = new int[n];
    	for(int i = 0; i <  n; i++)
    		a[i] = nextInt();
    	
    	return a;
    }
    
    public Long[] nextLongArray(int n) {
    	Long[] a = new Long[n];
    	for(int i = 0; i <  n; i++)
    		a[i] = nextLong();
    	
    	return a;
    }
    
    public long[] nextlongArray(int n) {
    	long[] a = new long[n];
    	for(int i = 0; i <  n; i++)
    		a[i] = nextLong();
    	
    	return a;
    }
    
    public double[] nextdoubleArray(int n) {
    	double[] a = new double[n];
    	for(int i = 0; i <  n; i++)
    		a[i] = nextDouble();
    	
    	return a;
    }
    
    public String[] nextStringArray(int n){
    	String[] s = new String[n];
    	for(int i = 0; i < n; i++)
    		s[i] = next();
    	return s;
    }
    
    public String[] nextLineStringArray(int n){
    	String[] s = new String[n];
    	for(int i = 0; i < n; i++)
    		s[i] = next();
    	return s;
    }

    
    }