#include <bits/stdc++.h>
using namespace std;
#define MAXN 1000000
int main() {
    int n, d;
    cin >>n>> d;
    int A[MAXN];
    for(int i=0; i< n; i++ ){
       cin>>A[i];
    }   
    int sum=0;
    for(int i=0; i< n; i++ ){
       int count=0;
	   if(A[i]==1){
       	  for(int j=i+d; j<n; j=j+d){
       	  	  if(A[j]==0) count++;
		  }
	   }
	   sum= max(sum, count);
	   if(A[i]==0&&A[i+d]==0) break;
    }  
    cout<<sum;
    return 0;
}

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

OSAyCgoxIDAgMSAwIDAgMSAwIDAgMQ==

9 2

1 0 1 0 0 1 0 0 1