#include <bits/stdc++.h>
#define fx first
#define sx0 second
#define pb push_back
typedef long long ll;
const int Max = 100006;
const int Inf = 2e9;
const int MOD = 666013;
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

deque <ll> q;

void add_in (ll a) {
	while (!q.empty() && q.back() > a) q.pop_back();
	q.push_back(a);
}

void remove (ll a) {
	if (q.front() == a) q.pop_front();
}

void solve () {
	ll n, k;
	in >> n >> k;
	ll a[n+6];
	for (int i=1; i<=n; i++) in >> a[i];
	ll ans = 0;
	for (ll i=1; i<=n; i++) {
		add_in(a[i]);
		if (i - k > 0) remove(a[i-k]);
		if (i >= k) ans += q.front();
	}
	out << ans << "\n";
	return;
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int t=1;
//	cin >> t;
	while (t--) {
		solve();
	}
	return 0;
}