#include <fstream>
#include <deque>
#include <vector>
using namespace std;
typedef int Int32;
typedef unsigned UInt32;
typedef long long Int64;

int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");

	UInt32 N,K;
	f>>N>>K;

	deque< pair<UInt32,Int64> > d;

	Int64 sum = 0L;
	for(UInt32 i=0u;i<N;++i)
	{
		Int64 x; f>>x;
		if(!d.empty() && i >= K && d.front().first == i - K)
			d.pop_front();
		while(!d.empty() && x < d.back().second)
			d.pop_back();
		d.push_back( pair<int,int>(i,x) );
		if(i >= K - 1)
			sum += d.front().second;
	}

	g << sum;
	return 0;
}