#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <iterator>
#include <random>
#include <assert.h>
using namespace std;

const string file = "deque";

const string infile = file + ".in";
const string outfile = file + ".out";

const int INF = 0x3f3f3f3f; 

//#define ONLINE_JUDGE

int main()
{
#ifdef ONLINE_JUDGE
	ostream &fout = cout;
	istream &fin = cin;
#else
	fstream fin(infile.c_str(), ios::in);
	fstream fout(outfile.c_str(), ios::out);
#endif	

    int N, K;
    fin >> N >> K;
    vector<int> A(N);
    for(int i = 0; i < N; i++)
        fin >> A[i];

    deque<pair<int, int> > deq;

    long long Sol = 0;


    for(int i = 0; i < N; i++)
    {
        if(deq.empty() == false && deq.front().second == i - K)
            deq.pop_front();
        while(deq.empty() == false && deq.back().first >= A[i])
        {
            deq.pop_back();
        }
        deq.push_back(make_pair(A[i], i));
        if(i >= K - 1)
        {
            Sol += deq.front().first;
        }
    }


    fout << Sol << "\n";




#ifdef ONLINE_JUDGE
#else
    fout.close();
	fin.close();
#endif
}