#include <fstream>
#include <iostream>
#include <string>
#include <complex>
#include <cmath>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <cstdio>
#include <stack>
#include <algorithm>
#include <list>
#include <bitset>
#include <ctime>
#include <cassert>
#include <iomanip>

using namespace std;


const string file = "trie";
const string inputF = file + ".in";
const string outputF = file + ".out";

const double epsilon = 1e-7;
#define LL long long
#define ULL unsigned long long 
#define MOD1 666013
#define MOD2 666019
#define MOD3 1999999973
#define base 73

typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<string> vs;
typedef pair<int, int> ii;
typedef pair<long long, long long> ll;
typedef vector<ii> vii;
typedef vector<ll> vll;

#define all(V) V.begin(), V.end()
#define allr(V) V.rbegin(), V.rend()
#define for_c_it(container, it) for (auto it : container)
#define present(container, element) (container.find(element) != container.end()) 
#define sz(a) int((a).size()) 
#define pb push_back 
#define mp make_pair
#define zeroes(x) ((x ^ (x - 1)) & x)

vi V;
deque<ii> dq;
int N, K;

int main() {
#ifndef INFOARENA
	freopen("input.txt", "r", stdin);
#else 
	freopen(inputF.c_str(), "r", stdin);
	freopen(outputF.c_str(), "w", stdout);
#endif
	int ans, i, x;
	scanf("%d %d", &N, &K);
	scanf("%d", &x);
	dq.pb(mp(x, 0));
	for (i = 1; i < K; ++i) { 
		scanf("%d", &x);
		while (!dq.empty() && dq.back().first >= x) {
			dq.pop_back();
		}
		dq.pb(mp(x, i));
	}
	ans = dq.front().first;
	for (i = K; i < N; ++i) {
		if (dq.front().second <= i - K) {
			dq.pop_front();
		}
		scanf("%d", &x);
		while (!dq.empty() && dq.back().first >= x) {
			dq.pop_back();
		}
		dq.pb(mp(x, i));
		ans += dq.front().first;
	}
	printf("%d", ans);
	return 0;
}