#include<stdio.h>
#include<deque>
using namespace std;

FILE*f=fopen("deque.in","r");
FILE*g=fopen("deque.out","w");

int N,K,i,X,A[5000100];
long long sol;
deque<int>deq;

int main () {
	
	fscanf(f,"%d %d",&N,&K);
	for( i = 0 ; i < N ; ++i ) {
		fscanf(f,"%d",&A[i]);
	}		
	
	deque<int>::iterator it;
	
	for( i = 0 ; i < N ; ++i ){
		
		while( !(deq.empty() ) && A[deq.back()] > A[i] )
			deq.pop_back();
		
		deq.push_back(i);
		
		if ( i - deq.front() >= K )
			deq.pop_front();
		
		if ( i >= K - 1 )
			sol += A[deq.front()];
		
	}
	
	fprintf(g,"%lld\n",sol);
	
	
	fclose(f);
	fclose(g);
	
	return 0;
	
}