#include <fstream>
using namespace std;
int n,k,a[5000000],d[5000000],s,e=-1;
long long S;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main()
{
	int i;
	fin>>n>>k;
	for(i=0;i<n;i++)
		fin>>a[i];
	for(i=0;i<n;i++)
	{
		while(s<=e && a[i]<=a[d[e]])
			e--;    
		d[++e]=i;
		if(d[s]==i-k)
			s++;
		if(i>=k)
			S+=a[d[s]];    
	}
    fout<<S<<"\n";
    return 0;
}