#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

#define maxn 5000010


ifstream f("deque.in");
ofstream g("deque.out");

template<typename T>
class Deque{

    private:
        vector<T> deque;

    public:

        void push_front(T x){
            deque.insert(deque.begin(), x);
        }

        void push_back(T x){
            deque.push_back(x);
        }

        void pop_back(){
            deque.pop_back();
        }

        void pop_front(){
            deque.erase(deque.begin());
        }

        T front(){
            return deque.front();
        }

        T back(){
            return deque.back();
        }

        size_t size(){
            return deque.size();
        }

        bool empty(){
            return deque.empty();
        }
};

int main()
{
	

    long long no_of_elements, interval, x, sum = 0, last = 1, last_index = 0;
    f >> no_of_elements >> interval;

    // Deque<pair<long long, long long>> deque;

	long long* numbers = new long long[maxn]; 
	long long* elements = new long long[maxn];


	for(long long i=1; i<=no_of_elements; i++){
		f >> x;
		elements[i] = x;
	}

    for(long long i=1; i<=no_of_elements; i++){

        while((last <= last_index && elements[i] <= elements[numbers[last_index]])){
			last_index--;    
        }

		numbers[++last_index] = i;

        if(numbers[last] == i - interval) last++;

        if(i >= interval){ 
            sum += elements[numbers[last]];
         }
    }

    g << sum;	

    return 0;
}