#include <iostream>
#include <fstream>
using namespace std;
 
ifstream F("deque.in");
ofstream G("deque.out");
 
const int N = 5000010;


template <class T>
class deque {
	private:
		struct node {
			T value;
			node *next;
			node *last;
		};
		node *front;
		node *back;
	
	
	public:
		deque() {
			front = back = nullptr;
		}
		
		void push_front(T value) {
			node *newNode = new node();
			newNode -> next  = front;
			newNode -> value = value;
			front = newNode;
			if ( back == nullptr ) back = front; 
		}
		
		void push_back(T value) {
			node *newNode = new node();
			newNode -> last  = back;
			newNode -> value = value;
			back = newNode;
			if ( front == nullptr ) front = back; 
		}
		
		T get_front() {
			return front -> value;
		}
		
		T get_back() {
			return back -> value;
		}
		
		void pop_front() {
			node *now = front;
			front = front -> next;
			delete now;
		}
		
		void pop_back() {
			node *now = back;
			back = back -> last;
			delete now;
		}
};
 
int n,k,a[N];
deque<int> dq;
long long ans;
 
int main()
{
    F>>n>>k;
    for (int i=1;i<=n;++i)
        F>>a[i];
    for (int i=1;i<=k;++i)
    {
        if ( !dq.empty() )
        {
            while ( a[i] < a[dq.back()] )
            {
                dq.pop_back();
                if ( dq.empty() ) break;
            }
        }
        dq.push_back( i );
    }
    ans += a[dq.front()];
    for (int i=k+1;i<=n;++i)
    {
        if ( !dq.empty() )
            if ( dq.front() <= i-k )
                dq.pop_front();
        if ( !dq.empty() )
        {
            while ( a[i] < a[dq.back()] )
            {
                dq.pop_back();
                if ( dq.empty() ) break;
            }
        }
        dq.push_back( i );
        ans += a[dq.front()];
    }
    G<<ans<<'\n';
}