#include<cstdio>
#define min(a, b) ((a) < (b) ? (a) : (b))

using namespace std;
long long n, k, s;
long long a[500001];

int main() {
	
	long long i, j;
	
	freopen("deque.in", "r", stdin), freopen("deque.out", "w", stdout);
	scanf("%lld %lld", &n, &k);
	
	for(i = 1; i <= n; i++)
		scanf("%lld", a + i);
	
	s = 0;
	for(i = 1; i <= n - k + 1; i++)
	{
		long long m = 10000001;
		for(j = i; j < i + k; j++)
			m = min(m, a[j]);
		s += m;
	}
	
	printf("%lld\n", s);
	
	return 0;
}