#include<fstream.h>
long n,k,i,j,x;
long long int v[500000],s=0,min;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
f>>n>>k;
for (i=0;i<n;i++) f>>v[i];
for (i=0;i<n-k+1;i++)
	{
	min=500001;
	for (j=i;j<i+k;j++)
		if (min>v[j]) min=v[j];
	s+=min;
	}
g<<s;
g.close();
return 0;
}