#include <fstream.h>
#define N 5000001

ifstream fin("deque.in");
ofstream fout("deque.out");

int n,k,s[N],deque[N],first,last;
long long sum=0;

int main(){
	int i,j;
	
	fin>>n>>k;
	
	for (i=1; i<=n; i++)
		fin>>s[i];
	
	
	first = 1;
	last  = 0;
	
	for (i=1; i<=n; i++){
		
		while ( first <= last && s[deque[last]] >= s[i]) last--;
		
		deque[++last] = i;
		
		if (deque[first] == i-k)			
			
			first++;
		
		
		if (i >= k ) sum+= s[deque[first]];
			
	
	}
	
	fout<<sum;;
	
	return 0;
}