#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
int p[3001];
vector<int>v;
int main()
{
int n, m;
cin >> n >> m;
for (int i = 0; i < n; i++)
	cin >> p[i];
int sum = 0, count = 0,t;
for (int i = 0; i < n-m; i++)
{
	t = i;
	while (count <m)
	{
		sum += p[t];
		count++;
		t++;
	}
	v.push_back(sum);
	sum = 0;
	count = 0;
}
sort(v.begin(), v.end());
cout << v[0];
return 0;
}