#include<fstream.h>
ifstream f("deque.in");
ofstream g("deque.out");
long long a[5000][5000],i,j,n,min,s,poz,k;
int main ()
{f>>n>>k;
 poz=n+1;
 for (i=0;i<n;i++) {f>>a[0][i];
						  for (j=1;j<=k;j++) a[j][i+1]=a[j-1][i];}
for (i=k-1;i<n;i++)
	{min=10000001;
	 for (j=0;j<k;j++)
		if (a[j][i]<min) min=a[j][i];
	 s+=min;}
 g<<s;
return 0;
}