#include <fstream>

using namespace std;

long keys[5000001]; 
long elements[5000001];
long no_of_elements, interval, x, sum = 0, last = 1, last_index = 0;


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


int main()
{
	

    f >> no_of_elements >> interval;

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

    for(long i=1; i<=no_of_elements; i++){
        if(last <= last_index && keys[last] == i - interval) 
			last++;

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


		
		keys[++last_index] = i;

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

    g << sum;	

    return 0;
}