#include <stdio.h>

int main() {
	int n, m, i, j, k, a[100], sum = 0;
	long long min = 10000000;
	scanf("%d%d", &n, &m);
	for (i = 0; i < n - 1; i++)
		scanf("%d\n", &a[i]);
	scanf("%d", &a[i + 1]);
	for (i = 0; i < n; i++) {
		sum = 0;
		for (j = i; j < i + m; j++) {
			sum = sum + a[j];
		}
		if (sum < min)
			min = sum;
	}
	printf("%d", min);
	return 0;
}