#include <bits/stdc++.h>
using namespace std;
struct meh
{
    int val,i;
}x;
deque <meh> q;
int k,n,s;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);

    for(int i=1;i<=k;i++)
    {
        scanf("%d",&x.val);
        x.i=i;
        while(!q.empty() && q.back().val>=x.val) q.pop_back();
        q.push_back(x);

    }
    s=q.front().val;
    for(int i=k+1;i<=n;i++)
    {
        scanf("%d",&x.val);
        x.i=i;
        while(!q.empty() && q.back().val>=x.val) q.pop_back();
        q.push_back(x);

        if(q.front().i<i-k+1) q.pop_front();

        s=s+q.front().val;
       // printf("%d\n",q.front().val);
    }
    printf("%d\n",s);
    return 0;

}