#include <cstdio>
#include <queue>

using namespace std;

int v[1000005];

typedef pair<int,int>ii;
deque <ii>q;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,i,k,s=0;
    scanf("%d %d",&n,&k);
    for (i=1;i<=n;i++)
         scanf("%d",&v[i]);
    for (i=1;i<=n;i++)
    {
        while(!q.empty() && q.back().first>=v[i])
              q.pop_back();

        q.push_back(ii(v[i],i));

        while(!q.empty() && i-q.front().second+1>k)
              q.pop_front();
        if (i>=k)
            s=s+q.front().first;
    }
    printf("%d\n",s);
    return 0;
}