#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,s,k,que[5000005],a[5000005],p,u;
int main()
{
    fin>>n>>k;
    p=1;
    u=0;
    for(int i=1;i<=n;i++)
    {
        fin>>a[i];
        while(p<=u && a[i]<=a[que[u]])
            u--;
        que[++u]=i;
        if(que[p]==i-k)
            p++;
        if(i>=k)
            s+=a[que[p]];
    }
    fout<<s;
    return 0;
}