# include <cstdio>
  using namespace std;
	  int n, k, i, first = 1, last, a[5000001], deque[5000001];
		long long s;
		
		int main ()
		{ freopen ("deque.in", "rt", stdin); freopen ("deque.out", "wt", stdout);
		  for (scanf ("%d%d", &n, &k), i = 1; i <= n; ++i) scanf ("%d", &a[i]);
			for (i = 1; i <= n; ++i)
			  { while (first <= last && a[i] <= a [deque [last]]) --last;
			    deque [++last] = i;
				  if (deque [first] == i - k) ++first;
					if (i >= k) s += a [deque [first]];
			  }
			printf ("%lld\n", s); return 0;
		}