9 13
6 14 19 5 -5 6 -10 20 8
 8 9
6 -1 5 -5 -8 -7 -8 -7
 10 7
-9 3 -4 -22 4 -17 0 -14 3 -2
 6 2
-2 3 0 -2 0 0
 5 10
-8 -24 0 -22 12
 5 13756
-2 -9 -10 0 10
 7 3
1 -3 0 3 -1 0 2
 9 9
-3 2 0 -2 -7 -1 0 5 3
 2 3
2 0
 19 78701
1 0 -1 0 -1 -1 0 1 0 -1 1 1 -1 1 0 0 -1 0 0
 5 4
-1 0 0 1 -1
 6 4
-1 0 2 -4 0 5
 20 23036
-1 1 -1 -1 -1 -1 1 -1 -1 0 0 1 1 0 0 1 0 0 -1 -1
 5 4
-1 0 -3 0 3
 12 82016
1 -2 -1 -1 -2 -1 0 -2 -1 1 -2 2
 7 4
-6 0 2 -3 0 4 0
 4 4
2 2 0 1
 6 1
-3 0 0 0 -2 3
 8 26
-4 9 -14 -11 0 7 23 -15
 20 23079
0 1 1 -1 1 0 -1 -1 0 0 1 -1 1 1 1 0 0 1 0 1
 1 1
1
 7 8555
-2 -3 -2 3 0 -2 0
 4 100
-100 0 -50 100
 3 14
12 12 -8
 1 1
2
 10 23
9 7 14 16 -13 -22 24 -3 -12 14
 8 11
12 -12 -9 3 -22 -21 1 3
 19 49926
-2 0 2 0 0 -2 2 -1 -1 0 0 0 1 0 1 1 -2 2 2
 16 76798
-1 11 -7 -4 0 -11 -12 3 0 -7 6 -4 8 6 5 -10
 9 5
-2 0 3 -4 0 4 -3 -2 0

-1
 -1
 1
 1
 1
 1
 -1
 2
 0
 1
 1
 -1
 1
 1
 1
 1
 -1
 1
 -1
 0
 0
 1
 1
 -1
 -1
 -1
 -1
 1
 1
 1

import java.util.*;
import java.io.*;
public class A
{
      public static void main(String ar[]) throws Exception
      {
            BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
            String s1[]=br.readLine().split(" ");
            int n=Integer.parseInt(s1[0]);
            long d=Long.parseLong(s1[1]);
            
            String s2[]=br.readLine().split(" ");
            long a[]=new long[n];
            for(int i=0;i<n;i++)
             a[i]=Long.parseLong(s2[i]);
            
            int u=-1;
            long S=0;
            long t=0;
            long v=0;
            for(int i=0;i<n;i++)
            {
                  if(a[i]==0)
                  {
                        long p=0;
                        if(S<0 && u==-1)
                        {
                              p=(long)Math.floor((double)S/d);
                              p=-1*p;
                              v=(S+p*d)%d;
                              S=0;
                        }
                        else if(S<0)
                        {
                              S=Math.min(0,S+v);
                              p=(long)Math.floor((double)S/d);
                              p=-1*p;
                              v=(S+p*d)%d;
                              S=0;
                        }
                        //System.out.println(p+" "+v);
                        if(p>0)
                        t++;
                         u=0;
                  }
                  else
                  {
                        S+=a[i];
                  }
                  if(S>d)
                  { t=-1; break;  }
                  v=Math.min(v,d-S);
            }
            
            System.out.println(t);
      }
}