#include <fstream>
#include <deque>
using namespace std;

int main() {
	ifstream fin("deque.in");
	ofstream fout("deque.out");
	int n, k;
	fin >> n >> k;
	int a[n];
	for (int i=0; i<n; ++i) fin >> a[i];
	deque<int> mayuse;
	long long sum=0;
	for (int i=0; i<n; ++i) {
		if (mayuse.front()<=i-k) mayuse.pop_front();
		while (!mayuse.empty() && a[i]<=a[mayuse.back()])
			mayuse.pop_back();
		mayuse.push_back(i);
		if (i>=k-1) sum+=a[mayuse.front()];
	}
	fout << sum;
	return 0;
}