#include<deque>
#include<cstdio>
using namespace std;
struct val
{
    int x,y;
};
deque<val>q;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,i,k,x1;
    long long s=0;
    val f;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    {
        if(q.front().y==i-k) q.pop_front();
        scanf("%d",&x1);
        while(q.empty()==0&&x1<=q.back().x)
            q.pop_back();
        f.x=x1;
        f.y=i;
        q.push_back(f);
        if(i>=k) s+=q.front().x;
    }
    printf("%lld",s);
    return 0;
}