#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[5000001],i,j,m,s;
int main(){
	f>>n>>k;
	for(i=1;i<=n;++i)
		f>>a[i];
	s=0;
	for (i=1;i<=n-k+1;++i)
	{m=a[i];
	for (j=1;j<=i+k-1;++j)
		if (a[j]<m) m=a[j];
	s+=m;
	}
	f<<s<<'\n';
	g.close();
	return 0;
}