#include <fstream>

#define qqL 5000001

using namespace std;

ifstream in;
ofstream out;

struct deque
{
    int val,pos;
}qq[qqL];

int main()
{
    int N,K,x;
    in.open("deque.in");

    in>>N>>K;

    long long sum=0;

    int head=1;
    int tail=0;

    for(int i=1;i<=N;++i)
    {
        in>>x;
        for(;x<=qq[tail].val&&head<=tail;--tail);
        qq[++tail].val=x;
        qq[tail].pos=i;

        if(qq[tail].pos-qq[head].pos>=K) ++head;
        if(i>=K) sum+=qq[head].val;
    }

    in.close();

    out.open("deque.out");

    out<<sum<<'\n';

    out.close();

    return 0;
}