#include <stdio.h>
#include <stdlib.h>
#define NMAX 5000001
int deque[NMAX],v[NMAX];

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k,i,x,st=1,dr=0;
    long long sum=0;
    scanf("%d %d",&n,&k);
    for (i=1;i<=n;i++)
    {
        scanf("%d",&x);
        while (st<=dr && i-v[st]>=k) st=st+1;
        while (st<=dr && x-deque[dr]<=0) dr=dr-1;
        deque[++dr]=x;
        v[dr]=i;
        if (i>=k) sum+=deque[st];
    }
    printf("%lld",sum);
    fclose(stdout);
    fclose(stdin);
    return 0;
}