#include <bits/stdc++.h>
#define startt ios_base::sync_with_stdio(false);cin.tie(0);
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
typedef unsigned long long ull;
typedef long long  ll;
using namespace std;
#define FOR(n) for(int i=0;i<n;i++)
#define vt vector
#define vint vector<int>
#define all(v) v.begin(), v.end()
#define MOD 1000000007
#define MOD2 998244353
#define MX 1000000000
#define nax 100005
#define MXL 1000000000000000000
#define PI 3.14159265
#define pb push_back
#define pf push_front
#define sc second
#define fr first
#define int ll
#define endl '\n'
#define ld long double

vector<int> read(int n) {vector<int> a; for (int i = 0; i < n; i++) { int x; cin >> x; a.pb(x);} return a;}


int32_t main(){
	startt;
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	deque<pair<int, int>> q;
	int n, k;
	cin >> n >> k;
	int cnt_added = 0;
	int cnt_removed = 0;
	int ans = 0;
	for(int i = 0; i < k; i++)
	{
		int el;
		cin >> el;
		while (!q.empty() && q.back().first > el)
		{
			q.pop_back();
		}
		q.push_back({el, cnt_added});
		cnt_added++;
	}
	ans+=q.front().fr;
	for(int i = k; i < n; i++)
	{
		int el;
		cin >> el;
		if (!q.empty() && q.front().second == i-k)
		{
			q.pop_front();
		}
		cnt_removed++;
		while (!q.empty() && q.back().first > el)
		{
			q.pop_back();
		}
		q.push_back({el, cnt_added});
		cnt_added++;
		ans+=q.front().fr;
	}
	cout << ans << endl;
}