#include <stdio.h>
 
#define maxn 5000010
#define inf 1000000000
 
int N, K;
int A[maxn];
long long Sum;
 
int main()
{
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
 
	int i, j, best;
 
	scanf("%d %d ", &N, &K);
 
	for (i = 1; i <= N; i++) scanf("%d ", &A[i]);
 
	for (i = 1; i <= N-K+1; i++)
	{
		best = inf;
		for (j = 0; j < K; j++)
			if (A[i+j] < best) best = A[i+j];
 
		Sum += best;
	}
 
	printf("%lld\n", Sum);
 
	return 0;
}