#include<cstdio>
#include<deque>
using namespace std;
const int N=5000005;
int v[N],n,k;
long long rez;
deque <int> q;

void read()
{
	scanf("%d%d",&n,&k);
	for( int i=1 ; i<=n ; ++i )
		scanf("%d",&v[i]);
}

void dreapta( int i )
{
	while(!q.empty() && v[i]<=v[q.back()])
		q.pop_back();
}

void stanga( int i )
{
	if( i-k == q.front() )
		q.pop_front();
}

void solve()
{
	for( int i=1 ; i<=n ; ++i )
	{
		dreapta(i);
		q.push_back(i);
		stanga(i);
		if(i>=k)
			rez+=v[q.front()];
	}
	printf("%lld",rez);
}

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	read();
	solve();
	return 0;
}