#include <fstream.h>
ifstream f("deque.in");
ofstream g("deque.out");
long long n,k,v[5000001];

int main()
{
	//n numere si sir de lungime k;
	int i,j,min,ming=0;
	f>>n>>k;
	for(i=1;i<=n;i++)
		f>>v[i];
	
	for(i=1;i<=n-k+1;i++)
	{
		min=5000001;
		for(j=i;j<=i+k-1;j++)
			if(v[j]<min)
				min=v[j];
		ming+=min;
	}
	g<<ming;
	f.close();
	g.close();
	return 0;
}