#include <iostream>
#include <fstream>
using namespace std;
int A[5000001], Deque[5000001];
int N,i,j,k;
long long Sum;
int Front,Back;
ifstream fin ("deque.in");
ofstream fout ("deque.in");
int main()
{
    fin>>N;
    fin>>k;
    for(i=1; i<=N; i++)
        fin>>A[i];
    Front=1;
    Back=0;
    for(i=1; i<=N; i++)
    {
        while(Front<= Back && A[i]<=A[Deque[Back]]) Back--;
        Deque[++Back]=i;
        if(Deque[Front]==i-k) Front++;
        if(i>=k) Sum+=A[Deque[Front]];
    }
fout<<Sum;
}