#include<stdio.h>

#define MAXN 5000002

int v[ MAXN ], deque[ MAXN ], n, k;
long long int s;

void read()
{
	FILE *f = fopen("deque.in", "r");
	
	fscanf(f, "%d %d", &n, &k);
	for(int i = 1; i <= n; i++)
		fscanf(f, "%d", &v[i]);
	
	fclose(f);
}

void solve()
{
	for(int i = 1, st = 1, end = 0; i <= n; i++)
	{
		while(v[i] <= v[ deque[end] ] && st <= end)
			end--;
		end++, deque[end] = i;
		
		if(deque[st] == i - k)
			st++;
		
		if(i >= k)
			s += v[ deque[st] ];
	}
}

void write()
{
	FILE *g = fopen("deque.out", "w");
	
	fprintf(g, "%lld\n", s);
	
	fclose(g);
}

int main()
{
	read();
	solve();
	write();
	return 0;
}