#include<stdio.h>
#include<limits.h>
#include<malloc.h>
long maxsum(int n,int k,long *profits,long maxprofit){
    long min = LONG_MAX;
    int i =0,j=0;
    int jump = k+1;
    for(i=0;i<jump;i++){
        long cursum = 0;
        for(j=i;j<n;j+=jump){
            cursum += profits[j];
        }
        if(cursum<min){
            printf("i = %d\n",i);
            min = cursum;
        }
    }
    return maxprofit - min;
}
int main(){
        int cases=0,casedone=0;
        int  n,k;
    long *array;
    long maxprofit = 0;
        fscanf(stdin,"%d %d",&n,&k);
        array = malloc(sizeof(long)*n);
      while(casedone < n){
                fscanf(stdin,"%ld",&array[casedone]);
            maxprofit += array[casedone];
        casedone++;
        }
    printf("%ld",maxsum(n,k,array,maxprofit));
}