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.*;
import java.math.BigInteger;
import java.text.DecimalFormat;
import java.util.*;
import java.lang.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class Contest {
	//static ArrayList<Integer> prime=new ArrayList();
	
	   public static TreeMap<Long,Integer> t1=new TreeMap();
	   public static void solve()
	    {
	      long m=1;
	      for(int j=2;j<=1000;j++)
	      {
	         
	          if(isprime(j))
	          {
	              m=m*j;
	              if(m>1000000)
	              {
	                  break;
	              }else{
	                  t1.put(m,1);
	              }
	          }
	      }
	    }
	
    public static int gcd(int n1, int n2)
    {
        if (n2 != 0)
            return gcd(n2, n1 % n2);
        else
            return n1;
    }
	
//////////////////	
	public static class trie {
        int x,y,z;
        trie (int x,int y,int z){
            this.x=x;
            this.y=y;
            this.z=z;
        }
	
	} 
        
	public static class pair {
        int x,y;
        pair (int x,int y){
            this.x=x;
            this.y=y;
        }
        public boolean equals(Object o) {
        	if(o instanceof pair) {
        		pair p = (pair)o;
        		return (x == p.x && y == p.y);
        	}
        	return false;
        }
        public int hashCode() {
        	return (Integer.hashCode(x) * 3 + Integer.hashCode(y) );
        }
    }
	
//////////////////	
	
	static class Cmp implements Comparator<pair>
	{
		public int compare(pair a,pair b)
		{
			if(a.x==b.x)
			{
				return(a.y-b.y);
			}
			return(a.x-b.x);
		}
	}
	
	
//////////////////
	
	
	
	
//////////////////
	
	
	
	
	
	   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; 
	        } 
	   }
	   
////////////////////// 
	//public static ArrayList<Integer> a=new ArrayList();
	   
	  public static ArrayList<Integer> Divisors(int n) 
	   { 
	       // Note that this loop runs till square root 
		  ArrayList<Integer> a=new ArrayList();
		   long sum=0;
	       for (int i=1; i*i<=(n); i++) 
	       { 
	           if (n%i == 0) 
	           { 
	               // If divisors are equal, print only one 
	               if (n/i == i) 
	               {
	                  // printf("%d ", i); 
	            	   sum=sum+1;
	            	   a.add(i);
	               }
	     
	               else // Otherwise print both 
	               {
	                   //printf("%d %d ", i, n/i); 
	            	   sum=sum+2;
	            	   a.add(i);
	            	   a.add(n/i);
	               }
	           } 
	       } 
	       return(a);
	   } 
	   
/////////////////////	  
	  
	  public static long SmallestPrimeDivisor(long n) 
	  { 
	      // if divisible by 2 
	      if (n % 2 == 0) 
	          return 2; 
	    
	      // iterate from 3 to sqrt(n) 
	      for (long i = 3; i * i <= n; i += 2) { 
	          if (n % i == 0) 
	              return i; 
	      } 
	    
	      return n; 
	  } 
	    
////////////////////	  
	   
	   public static boolean isprime(long n)
	    {
	        int count=0;
	     
	        for(long i=2;i*i<=n;i++)
	        {
	            if(n%i==0)
	            {
	                return(false);
	            }
	        }
	        return(true);
	    }
	
	   
//////////////////////
	   
	     //   (x^n)%1000000007
	   public static long modularExponentiation(long x,long n,long M)
	   {
	       if(n==0)
	           return 1;
	       else if(n%2 == 0)        //n is even
	           return modularExponentiation((x*x)%M,n/2,M);
	       else                             //n is odd
	           return (x*modularExponentiation((x*x)%M,(n-1)/2,M))%M;

	   }
	   
	   public static long nCr(int n,int k)
	   {
		  if(k==0)
			  return 1;
		  return(n*nCr(n-1,k-1)/k);
	   }
	   public static long factorial(int n)
	   {
		   if(n==1)
			   return 1;
		   return((n)*factorial(n-1));
	   }
	   
	   public static void debug(Object...o) {
		    System.out.println( Arrays.deepToString(o) );
	   }
	   
	   public static boolean prime[]=new boolean[100005];
	   //prime[j]==false means it's a prime.
	   public static void seive()
	   {
		   prime[0]=false;
		   prime[1]=false;
		   for(int i=2;i*i<=100005;i++)
		   {
			   if(!prime[i])
			   {
				   for(int j=i*i;i<=100005;j+=i)
				   {
					   prime[j]=true;
				   }
			   }
		   }
	   }
	 
	 
	    public static boolean equals(StringBuilder sb1, StringBuilder sb2){
	    
	        if(sb1 == sb2)
	  
	        if(sb1 == null || sb2 == null)
	            return false;
	        
	        boolean isEqual = true;
	  
	        if(sb1.length() == sb2.length()){
	  
	            for(int i = 0 ; i < sb1.length(); i++){
	                
	                if(sb1.charAt(i) != sb2.charAt(i)){
	                    isEqual = false;
	                    break;
	                }
	            }
	            
	        }else{
	            isEqual = false;
	        }
	        
	        return isEqual;
	    }
	   
	    
	    public static boolean IsPalindrome(String s,int n)
	    {
	    	
	    	for(int i=0;i<n/2;i++)
	    	{
	    		if(s.charAt(i)!=s.charAt(n-i-1))
	    		{
	    			return false;
	    		}
	    	}
	    	return true;
	    }
	   
	   
	   
	   
	    
		public static void main(String []args) throws Exception
		{
			
			
			 FastReader in =new FastReader();	
			 PrintWriter pw = new PrintWriter(System.out);
		    //Scanner sc=new Scanner(System.in)
		    
		
			 int n=in.nextInt();
			 int m=in.nextInt();
			 int d=in.nextInt();
			// int a[][]=new int[n][m];
			 int a[]=new int[n*m];
			 int size=n*m;
			 for(int i=0;i<size;i++)
			 {
				a[i]=in.nextInt(); 
			 }
			 Arrays.parallelSort(a);
			 if(size%2==1)
			 {
				 int x=size/2;
				 long ans=0;
				 int m1=0;
				 for(int i=0;i<size;i++)
				 {
					 int y=Math.abs(a[i]-a[x]);
					 if(y%d==0)
					 {
						ans=ans+(y/d); 
					 }
					 else
					 {
						 m1=1;
						 break;
					 }
				 }
				 if(m1==1)
				 {
					 pw.println(-1);
				 }
				 else
				 {
					 pw.println(ans);
				 }
			 }
			 else
			 {
				 int x1=size/2;
				 int x2=x1-1;
				 long ans1=0,ans2=0;
				 
				 int m1=0,m2=0;
				 for(int i=0;i<size;i++)
				 {
					 int y=Math.abs(a[i]-a[x1]);
					 if(y%d==0)
					 {
						ans1=ans1+(y/d); 
					 }
					 else
					 {
						 m1=1;
						 break;
					 }
				 }
				// pw.println("ans1 "+ans1);
				  if(m1==1)
				  {
					  ans1=Long.MAX_VALUE-1;
				  }
				 for(int i=0;i<size;i++)
				 {
					 int y=Math.abs(a[i]-a[x2]);
					 if(y%d==0)
					 {
						ans2=ans2+(y/d); 
					 }
					 else
					 {
						 m2=1;
						 break;
					 }
				 }
				  // pw.println(ans2);
				 if(m1==1 && m2==1)
				 {
					 pw.println(-1);
				 }
				 else
				 {
					 pw.println(Math.min(ans1, ans2));
				 }

			 }
			 
			 
			 
			 pw.flush();
			 pw.close();
		   			
		}
			
	}	
		
		
		
		
		
		
		
		
		
		
	

