//
#include<stdio.h>
FILE *f=fopen("deque.in","r"), *g=fopen("deque.out","w");
long v[5000001],s,n,k,best,i,j;

int main()
{
	int i;
	
	fscanf(f,"%d %d", &n, &k);
	
	for(i=1;i<=n;i++)
		fscanf(f,"%d", &v[i]);
	
	 
    for (i =1;i<=n-k+1; i++)
    {
       best=100000000;
        for (j=0;j<k;j++)
           if (v[i+j] < best) best = v[i+j];

        s += best;
    }

fprintf(g,"%d",s);

fclose(f);
fclose(g);
return 0;
}