#include<cstdio>
#include<cstdlib>
int main()
{   
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int i,n,k,v[5000000],deq[5000000],f,b;
    long long s=0;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    scanf("%d",&v[i]);
    f=1;b=0;
    for(i=1;i<=n;i++)
    {
        while(f<=b && v[i]<=v[deq[b]])
            b--;
        deq[++b]=i;
        if(deq[f]==i-k) f++;
        if(i>=k) s+=v[deq[f]];
    }
    printf("%lld",s);
    return 0;
}