#include <fstream>
using namespace std;
int v[5000500];
int dq[5000500];

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n,k,i,vfs=0,vfd=0;
    long long s=0;
    in>>n>>k;
    for(i=1;i<=n;++i){
      in>>v[i];
      while(vfd>=vfs && v[dq[vfd]]>v[i]) vfd--;
      dq[++vfd]=i;
      if(i-dq[vfs]==k) ++vfs;
      if(i>=k) s=s+v[dq[vfs]];
    }
    out<<s;
    return 0;
}