#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(), (c).end()
#define pb push_back 
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;



int main() {
	std::ios::sync_with_stdio(false); cin.tie(NULL);
	int n, k; cin >> n >> k;
	vector<int> a(n);

	for(int i = 0; i < n; i++)
		cin >> a[i];

	multiset<ll> s;

	for(int i = 0; i < k; i++)
		s.insert(a[i]);

	ll ans = *s.begin();

	int l = 1;
	while(l+k-1 < n) {
		int r = l+k-1;
		s.erase(s.find(a[l-1]));
		s.insert(a[r]);
		ans += *s.begin();
		l++;
	}

	cout << ans << "\n";
	
	return 0;
}