#include <cstdio>

using namespace std;

#define nmax 5000001

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

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    int i;

    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;
}