#include<stdio.h>
#include<limits.h>
#define ll long long
int main()
{
	ll n,m,sum=0,min=INT_MAX,arr[3010]={0},j=1;
	scanf("%lld %lld",&n,&m);
	for(int i=1;i<=n;i++)
	{
		scanf("%lld",&arr[i]);
	}
	while(arr[j]!=0)
	{
		sum+=arr[j];
		if(j%m==0||j==n)
		{
			if(sum<min) 
			{
			    min=sum;
			}
			sum=0;
		}
		j++;
	}
	printf("%lld",min);
	return 0;
}