#include <iostream>
#include <cstdio>
#include <string.h>
#define inf 0x3f3f3f3f3f3f3f3f
using namespace std;

int n,k;
int v[5000010],deque[5000010];
long long suma;
int j;
int front;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    front=1;j=0;
    for (int i=1;i<=n;i++)
    {
        scanf("%d",&v[i]);
        while (v[i]<=v[deque[j]] && j>=front)
            j--;
        deque[++j]=i;
        if (deque[front]==i-k)
            front++;
        if (i>=k)
            suma+=v[deque[front]];
    }
    printf("%lld",suma);
    return 0;
}