#include <iostream>
#include<stdio.h>
using namespace std;
FILE *f=fopen("deque.in","r");
FILE *g=fopen("deque.out","w");
int n,k,i,j,A[5000010],Deque[5000010],mn,Front,Back;
long long s=0;
int main()
{
   fscanf(f,"%d%d",&n,&k);
   for(i=1;i<=n;i++) fscanf(f,"%d",&A[i]);
   Front=1;Back=0;
   for(i=1;i<=n;i++)
   {
       while(Front<=Back && A[i]<=A[Deque[Back]]) Back--;
       Deque[++Back]=i;
       if(Deque[Front]==i-k) Front++;
       if(i>=k) s+=A[Deque[Front]];
   }
   fprintf(g,"%d\n",s);

}