# include <stdlib.h>
# include <cstdio>

using namespace std;

int a[5000005], deque[5000005], back, front, n, k;
long long sum;

int main()
{int i;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    
    scanf("%d%d",&n,&k);
    
    for (i = 1; i <= n; i++)
    scanf("%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) sum += a[deque[front]];
        }
    printf("%lld",sum);
    
return 0;
}