#include <cstdio>
#include <deque>

#define N 5000000

using namespace std;

int v[N];

deque <int> q;

int main()
{

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

    int n,k;
    scanf("%d %d",&n,&k);

    int s=0;
    for(int i=0;i<n;++i)
    {
        scanf("%d",&v[i]);

        if(i - q.front()==k) q.pop_front();
        while(!q.empty() && v[q.back()]>=v[i])
            q.pop_back();

        q.push_back(i);

        if(i>=k-1) s+=v[q.front()];

    }

    printf("%d\n",s);
    return 0;
}