#include <stdio.h>
int s, n, k;
int main()
{
 int x, j, min;
 FILE *fi=fopen("deque.in", "r"), *fo=fopen("deque.out", "w");
 fscanf(fi, "%d%d", &n,&k);
 for(;n;n--)
  {
   fscanf(fi, "%d", &min);
   for(j=2; (j<=k)&&(n); j++,n--)
    {
     fscanf(fi, "%d", &x);
     min=min<x?min:x;
    }
   s+=min;
  }
 fprintf(fo, "%d", s);
 fclose(fi);
 fclose(fo);
 return 0;
}