#include <fstream>



using namespace std;

ifstream f("deque.in");

ofstream g("deque.out");

long long i,fr,ba,s,n,k;

int v[5*1001*1001],dq[5*1001*1001];

int main()

{

f>>n>>k;

for(i=1;i<=n;i++) f>>v[i];;

   fr=1;

   ba=0;

   for(i=1;i<=n;i++){

    while(fr<=ba&&v[i]<=v[dq[ba]]) ba--;

    dq[++ba]=i;

    if(dq[fr]==i-k) fr++;

if(i>=k) s+=v[dq[fr]];







   }

   g<<s;

    return 0;

}