#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;
}