#include <iostream>
#include <fstream>

using namespace std;


int N,K;
int A[5000000], Deque[5000000];
int Front, Back;
long long sum;

int main()
{
    ifstream input ("deque.in");
    ofstream output ("deque.out");

    input>>N>>K;

    for (int i=0; i<N; i++)
        input>>A[i];

    Front =0;
    Back =-1;
    for (int i=0; i<N; i++)
    {
        while(Front<=Back && A[i]<=A[Deque[Back]])
            Back--;

        Deque[++Back]=i;

        if(Deque[Front]==i-K)
            Front++;

        if (i>=K-1)
            sum+=A[Deque[Front]];
    }

    output<<sum;

    return 0;
}