#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>
using namespace std;

const string file = "deque";

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

const int INF = 0x3f3f3f3f;
int N, K;
vector<int> A;
long long Sol;
int main()
{
	fstream fin(infile.c_str(), ios::in);
	fin >> N >> K;
	A.resize(N);
	for(int i = 0; i < N; i++)
	{
		fin >> A[i];
	}
	fin.close();


	deque<int> deq;
	for(int i = 0; i < N; i++)
	{
		while(deq.empty() == false && A[deq.back()] >= A[i])
		{
			deq.pop_back();
		}
		deq.push_back(i);


		if(deq.front() <= i - K)
			deq.pop_front();

		if(i >= K - 1)
		{
			Sol += A[deq.front()];
		}
	}


	fstream fout(outfile.c_str(), ios::out);
	fout << Sol << "\n";
	fout.close();
}