#include <cstdio>

const int maxn=5000010;

int a[maxn], deque[maxn], i, k, n, first, last;
long long s;

int main()
{
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);

	scanf("%d%d", &n, &k);

	for(i=1; i<=n; ++i) scanf("%d", &a[i]);

	first=1, last=0;
	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;
}