#include <stdio.h>
#include <stdlib.h>

typedef struct Nr
{
	int val, poz;
}nr;
nr c[5000001];



int main()
{
	FILE *in = fopen("deque.in", "r"), *out = fopen("deque.out", "w");
	int n, k, i, x, inc = 0, sf = 0; 
	long long sum = 0;
	
	fscanf(in, "%d%d", &n, &k);
	fscanf(in, "%d", &x);
	c[1].val = x; c[1].poz = 1; //sum += x;
	for (i=2;i<=n;i++)
	{
		fscanf(in, "%d", &x);
		while (x <= c[sf].val && sf >= inc) sf--;
		c[++sf].val = x; c[sf].poz = i;
		if (c[inc].poz + k <= i) inc++;
		if (i >= k) sum += c[inc].val;
	}
	
	fprintf(out, "%lld", sum);
	return 0;
}