# include <stdio.h>
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;
}