#include<iostream>
#include<fstream>
#define maxn 5000010
using namespace std;
 
int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long sum;
 
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int i;
    f>>N>>K;
    
    for (i=1; i<=N; i++)
        f>>A[i];
 
    Front=1; Back=0;
 
    for (i=1; i<=N; i++){
        while (Front<=Back && A[i]<=A[ Deque[Back] ])
            Back--;
       
        Back++;
        Deque[Back] = i;
 
     
        if (Deque[Front]==i-K)
            Front++;
 
      
        if (i>=K) sum+=A[ Deque[Front]];
    }
 
    g<<sum;
    f.close();
    g.close();
    return 0;
}