#include<fstream>
using namespace std;
const int N=5000001;
int d[N],v[N],n,k,st,dr=-1;
long long s;
ifstream in("deque.in");
ofstream out("deque.out");
inline void stanga(int i)
{
	if(i-d[st] ==k)
		++st;
}
inline void dreapta(int i)
{
	while(st<=dr && v[d[dr]] >= v[i])
		dr--;
}
inline void adauga(int i)
{
	d[++dr] =i;
}
int main()
{
	int i;
	in>>n>>k;
	for(i=1;i<=n;++i)
		in>>v[i];
	for(i=1;i<=k;++i)
	{
		dreapta(i);
		adauga(i);
	}
	s+=v[d[st]];
	for(;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		s+=v[d[st]];
	}
	out<<s<<"\n";
	return 0;
}