#include <iostream>
#include <cstdio>
using namespace std;
int a[3001];
int main() {
int n, m;
cin >> n >> m;
for (int i = 0; i < n; i++) {
cin >> a[i];
}
int min = 1000000;
for (int i = 0; i < n - m; i++) {
int sum = 0;
for (int j = i; j < m + i; j++) {
sum += a[j];
}
if (sum < min) {
min = sum;
}
}
cout << min;
}