#include<iostream>
#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("degue.out");
#define nn 500000
#define xii 100000000
int main()
{
	int a[nn],i,n,k,j=1,s=0,min;
	f>>n>>k;
	for(i=1;i<=n;i++)
		f>>a[i];
	while(k<=n)
	{
		min=xii;
		for(i=j;i<=k;i++)
		{
			if(a[i]<min)
				min=a[i];
		}
		s=s+min;
		j++;
		k++;
	}
	g<<s;
	f.close();
	g.close();
	return 0;
}