#include <stdio.h>
#include <stdlib.h>
FILE*f;
FILE*g;
#define maxn 5000001
int A[ maxn ],deq[ maxn ], poz[ maxn ];
long long s;
int n,k,i,st,dr;
int main()
{   
    
    
    f=fopen("deque.in","r");
    g=fopen("deque.out","w");
    fscanf(f,"%d%d",&n,&k);s=0;
    for (i=1;i<=n;i++)
        fscanf(f,"%d",&A[i]);
    st=1;dr=0;
    for (i=1;i<=n;i++)
    {   while ((A[i]<=deq[dr]) && (st<=dr))
              dr--;
         deq[++dr]=A[i];
		 poz[dr] = i;
         if (poz[st]==i-k) st++;
         if (i>=k) s=s+deq[st];
         }
    fprintf(g,"%lld",s);
    return 0;
}