#include<fstream>
#define NMAX 5000010
using namespace std;
int V[NMAX],Deque[NMAX],P,U,N,K;
long long S;
int main()
{   ifstream f("deque.in");
ofstream g("deque.out");
   int i;
   f>>N>>K;
   for(i=1;i<=N;i++)
   f>>V[i];
   P=1;U=0;
   for(i=1;i<=N;i++)
     { while((P<=U)&& (V[i]<=V[Deque[U]]))
         U--;
         Deque[++U]=i;
         if(Deque[P]==i-K)  P++;
         if(i>=K)  S+=V[Deque[P]];
         } 
         g<<S;
         return 0;
        
         }