/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on May 9, 2010, 11:43 AM
 */
#include <deque>
#include <cstdlib>
#include <fstream>
#define Nmax 5000011

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