This morning, Roman woke up and opened the browser with n opened tabs numbered from 1 to n. There are two kinds of tabs: those with the information required for the test and those with social network sites. Roman decided that there are too many tabs open so he wants to close some of them.

He decided to accomplish this by closing every k-th (2 ≤ k ≤ n - 1) tab. Only then he will decide whether he wants to study for the test or to chat on the social networks. Formally, Roman will choose one tab (let its number be b) and then close all tabs with numbers c = b + i ⋅ k that satisfy the following condition: 1 ≤ c ≤ n and i is an integer (it may be positive, negative or zero).

For example, if k = 3, n = 14 and Roman chooses b = 8, then he will close tabs with numbers 2, 5, 8, 11 and 14.

After closing the tabs Roman will calculate the amount of remaining tabs with the information for the test (let's denote it e) and the amount of remaining social network tabs (s). Help Roman to calculate the maximal absolute value of the difference of those values |e - s| so that it would be easy to decide what to do next.

Input

The first line contains two integers n and k (2 ≤ k < n ≤ 100) — the amount of tabs opened currently and the distance between the tabs closed.

The second line consists of n integers, each of them equal either to 1 or to -1. The i-th integer denotes the type of the i-th tab: if it is equal to 1, this tab contains information for the test, and if it is equal to -1, it's a social network tab.

Output

Output a single integer — the maximum absolute difference between the amounts of remaining tabs of different types |e - s|.

Examples

Input


4 2
1 1 -1 1


Output


2


Input


14 3
-1 1 -1 -1 1 -1 -1 1 -1 -1 1 -1 -1 1


Output


9

Note

In the first example we can choose b = 1 or b = 3. We will delete then one tab of each type and the remaining tabs are then all contain test information. Thus, e = 2 and s = 0 and |e - s| = 2.

In the second example, on the contrary, we can leave opened only tabs that have social networks opened in them.
import java.io.*;
import java.util.*;
import java.math.*;
import java.lang.*;
 
import static java.lang.Math.*;
 
public class fast implements Runnable {
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
        private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
        
        public int read() {
            if (numChars==-1) 
                throw new InputMismatchException();
            
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                }
                catch (IOException e) {
                    throw new InputMismatchException();
                }
                
                if(numChars <= 0)               
                    return -1;
            }
            return buf[curChar++];
        }
     
        public String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
        public int nextInt() {
            int c = read();
            
            while(isSpaceChar(c)) 
                c = read();
            
            int sgn = 1;
            
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            
            int res = 0;
            do {
                if(c<'0'||c>'9') 
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c)); 
            
            return res * sgn;
        }
        
        public long nextLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
                return res * sgn;
        }
        
        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }
        
        public String readString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } 
            while (!isSpaceChar(c));
            
            return res.toString();
        }
     
        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
     
        public String next() {
            return readString();
        }
        
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
	
	class pair implements Comparable<pair>{
		int x;
		int y;
		pair(int xi, int yi){
			x=xi;
			y=yi;
		}
		@Override
		public int compareTo(pair other){
			int sum1=this.x+this.y, sum2=other.x+other.y;
			if(sum1>sum2){ return 1;}
			else if(sum1<sum2){ return -1; }
			else if(this.x>other.x){ return 1; }
			return 0;
		}	
	}

	class dist{
		int x;
		int y;
		int d;
		dist(int xi, int yi, int di){
			x=xi;
			y=yi;
			d=di;
		}
	} 
	
    public static void main(String args[]) throws Exception {
        new Thread(null, new fast(),"fast",1<<26).start();
    }
	
	public void sortbyColumn(int arr[][], final int col){ 
        // Using built-in sort function Arrays.sort 
        Arrays.sort(arr, new Comparator<int[]>() { 
            
          @Override              
          // Compare values according to columns 
          public int compare(final int[] entry1,  
                             final int[] entry2) { 
  
            // To sort in descending order revert  
            // the '>' Operator 
            if (entry1[col] > entry2[col]) 
                return 1; 
            else if(entry1[col] < entry2[col])
                return -1;
			return 0;
          } 
        });  // End of function call sort(). 
    }
	
	public void sortbyColumn(long arr[][], final int col){ 
        // Using built-in sort function Arrays.sort 
        Arrays.sort(arr, new Comparator<long[]>() { 
            
          @Override              
          // Compare values according to columns 
          public int compare(final long[] entry1,  
                             final long[] entry2) { 
  
            // To sort in descending order revert  
            // the '>' Operator 
            if (entry1[col] > entry2[col]) 
                return 1; 
            else if(entry1[col] < entry2[col])
                return -1;
			return 0;
          } 
        });  // End of function call sort(). 
    }
	
	long power(long x, long y, long p){  
        long res = 1;      
        x = x % p;  
        while (y > 0) 
        { 
            if((y & 1)==1) 
                res = (res * x) % p; 
            y = y >> 1;  
            x = (x * x) % p;  
        } 
        return res; 
    }

	long ncr(int n, int r, long p){  
        long C[]=new long[r+1]; 
        C[0] = 1; 
        for (int i = 1; i <= n; i++) 
        { 
            for (int j = Math.min(i, r); j > 0; j--) 
                C[j] = (C[j] + C[j-1])%p; 
        } 
        return C[r]; 
    }	
	
    public void run(){
        InputReader s = new InputReader(System.in);
        PrintWriter w = new PrintWriter(System.out);
		
		int n=s.nextInt(),k=s.nextInt(),a[]=new int[n],c1,c2,max=0,con1=0,con2=0;
		for(int i=0;i<n;i++){
			a[i]=s.nextInt();
			if(a[i]==1){
					con1++;
				}
			else con2++;
		}
		for(int b=0;b<n;b++){
			c1=0;
			c2=0;
			for(int i=b;i<n;i+=k){
				if(a[i]==1){
					c1++;
				}
				else c2++;
			}
			for(int i=b-k;i>=0;i-=k){
				if(a[i]==1){
					c1++;
				}
				else c2++;
			}
			if(abs(con1-c1-con2+c2)>max){max=abs(con1-c1-con2+c2);}
		}
		w.println(max);
		
		w.close();
    }
}