/* 
 * File:   main.cpp
 * Author: VirtualDemon
 *
 * Created on April 9, 2010, 4:23 PM
 */
#include <deque>
#include <vector>
#include <cstdlib>
#include <fstream>
#include <iterator>

/*
 * 
 */
using namespace std;
deque< int > DQ;
vector< int > v;
int main(int argc, char** argv)
{
    int N, K, i;
    long long int s=0;
    ifstream in( "deque.in" );
    in>>N>>K;
    copy( istream_iterator<int>(in), istream_iterator<int>(), back_inserter(v) );
    for( s=i=0; i < N; ++i )
    {
        for( ; !DQ.empty() && v[i] <= v[DQ.back()]; DQ.pop_back()  );
        DQ.push_back(i);
        if( i >= K-1 )
            s+=v[ DQ.front() ];
        if( DQ.front() == i-K+1 )
            DQ.pop_front();
    }
    ofstream out( "deque.out" );
    out<<s<<'\n';
    return EXIT_SUCCESS;
}