#include <cstdio>

using namespace std;

int v[5000001] , dq[5000001] , p , u , n , k;
long long sum;

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d %d",&n,&k);
	p = 1;
	for(int i=1;i<=n;++i)
	{
		scanf("%d",&v[i]);
		while(p<=u && v[i]<=v[dq[u]]) u--;
		dq[++u] = i;
		if(dq[p]==i-k) ++p;
		if(i>=k) sum+=v[dq[p]];
	}
	printf("%lld\n",sum);
	return 0;
}