#include <fstream>

using namespace std;

#define maxn 5000000
long numbers[maxn]; 
long elements[maxn];


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


int main()
{
	

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

	


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

    for(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;
}