#include <cstdio>
#include <vector>
#include <string.h>
#include <algorithm>
using namespace std;

vector <long> coada, coad2;

long N, K, s, i, j, a[5000001], minim;

int main() {
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	
		scanf("%ld %ld", &N, &K);
		
		for (i = 1; i <= N+1; ++i) {
			scanf("%ld", &a[i]);
			if (i >= K) {
				minim = 10000;
				for (j = i; j >= i-K+1; --j) {
					if (minim > a[j]) {
						minim = a[j];
					}
				}
				s += minim;
			}
		}
		
		printf("%ld\n", s);
	
	return 0;
}