#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> a(n);
    vector<int> b(n, 305);
    for (int i = 0; i < n; ++i)
    {
        cin >> a[i];
        if (i > (m-2))
        {
            int resum = 0;
            for (int j = 0; j < m; ++j)
            {
                if(i-j<0) break;
                resum += a[i - j];
                
            }
            b[i] = resum;
        }
    }
    sort(b.begin(), b.end());
    cout << b[0];
    return 0;
}