#include <bits/stdc++.h>
using namespace std;

#define problem "deque"
#define NMAX 5000005

int v[NMAX];

int main()
{
	FILE *f = fopen(problem ".in", "r");
	
	int n, k;
	fscanf(f, "%d%d", &n, &k);

	for (int i = 1; i <= n; ++i)
		fscanf(f, "%d", &v[i]);
	
	fclose(f);

	long long ans = 0;
	deque<int> dq;

	for (int i = 1; i <= n; ++i) {
		while (!dq.empty() && v[dq.back()] >= v[i])
			dq.pop_back();
		while (!dq.empty() && dq.front() <= i - k)
			dq.pop_front();
		dq.push_back(i);
		ans += (i >= k) * v[dq.front()];
	}

	f = fopen(problem ".out", "w");

	fprintf(f, "%lld\n", ans);

	fclose(f);
}