#include <fstream>

using namespace std;

#define MAX_N 5000010

int a[MAX_N],deque[MAX_N],n,i,k,x;
long long sum=0;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");

    int fata=1,spate=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
    for(i=1;i<=n;i++)
            {
              while(fata<=spate && a[i]<=a[deque[spate]]) spate--;
                deque[++spate]=i;
              if(deque[fata]==i-k) fata++;
              if(i>=k)  sum+=a[deque[fata]];
            }
    fout<<sum;
    fin.close();
    fout.close();
    return 0;
}