#include <stdio.h>

#define maxn 5000010
#define inf 1000000000
FILE *f,*g;

int N, K;
int a[maxn];
long long Sum;

int main()
{
	fopen("deque.in", "r");
	fopen("deque.out", "w");

	int i, j, best;

	fscanf(f,"%d %d ", &N, &K);

	for (i = 1; i <= N; i++) fscanf(f,"%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;
	}

	fprintf(g,"%lld\n", Sum);

	return 0;
}