#include <iostream>
#include <vector>
#include <climits>
using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    
    vector<int> a(n + 1);
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
    }
    
    int sum = 0;
    for (int i = 1; i <= m; ++i) {
        sum += a[i];
    }
    
    int min_sum = sum;
    for (int i = m + 1; i <= n; ++i) {
        sum = sum - a[i - m] + a[i];
        min_sum = min(min_sum, sum);
    }
    
    cout << min_sum << endl;
    return 0;
}