#include <iostream>
#include <fstream>

using namespace std;

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

int keys[5000005]; 
int elements[5000005];
int no_of_elements, interval, x, last = 1, last_index = 0;

long long sum = 0;
int main()
{
	
    f >> no_of_elements >> interval;

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

    for(int 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;
}