#include<stdio.h>
#define Nmax 5000003
FILE*f=fopen("deque.in","r");
FILE*g=fopen("deque.out","w");
int a[Nmax], q[Nmax],n,k;
long long s;
int main()
 {
 int p=1,u;
 u=0;
 fscanf(f,"%d %d",&n,&k);
 int i;
 for(i=1;i<=n;++i) fscanf(f,"%d",&a[i]);
 for(i=1;i<=n;++i)
  {
  //elimin ce am la sf
  while(p<=u && a[i] <= a[q[u]]) --u;
  //inserez
  q[++u]=i;
  //elim la inceput
  if(i-k == q[p]) ++p;
  if(i>=k) s+=a[q[p]];
  }
 fprintf(g,"%lld\n",s);
 return 0;
 }