#define x first
#define y second
#include <deque>
#include <cstdio>
using namespace std;

deque < pair < long , long long > > D;
const int Dim = 5000001;
long long n,k;
long long sum;
void Get (long long &x);

int main() {

	freopen("deque.in", "r" , stdin);
	freopen ("deque.out" , "w" , stdout);

	Get(n); Get(k);
	for ( int i = 1; i <= n; ++i) {
	long long q;
	Get(q);
	  while ( !D.empty() and D.front().x > q )
            D.pop_front();
        D.push_front({q,i});

        if ( i - D.back().y >= k ) D.pop_back();

        if (i >= k)
        sum += D.back().x;
        }
    printf("%d", sum);
}

const int Lim = 1000000;
int  u = Lim - 1;
char s[Lim];

void Next() {

	if ( ++u == Lim)
		fread(s,1,Lim,stdin) , u = 0;

}

void Get (long long &x) {
 bool semn = false;
    for (; s[u] < '0' || s[u] > '9'; Next());
    for (x = 0; s[u] >= '0' && s[u] <= '9'; Next())
       { if ( s[u-1] == '-')
			semn = true;
		   x = x * 10 + s[u] - '0';
		}
if( semn == true)
	x*=-1;
}