# include <cstdio>
# include <algorithm>
  using namespace std;
	  int m, n, k, a[1000000], i, w;
		long long s;
		int main ()
		{ freopen ("deque.in", "rt", stdin);
		  freopen ("deque.out", "wt", stdout);
			scanf ("%d%d", &n, &k);
		  for (i = 1; i <= n; ++i) scanf ("%d", &a[i]);
			for (w = 1; w <= n - k + 1; ++w)
			{ m = *min_element(a + w, a + w + k);
			  s = s + m;
		  }
			printf ("%lld\n", s);
		}