#include <iostream>
#include <vector>
#include <cmath>
using namespace std;
vector <int> t, aLenyeg, os;
int n, k;
void be() {
    cin >> n >> k;
    t.resize(n + 1);
    os.resize(n + 1);
    aLenyeg.resize(n + 1);
    for (int i = 1; i <= n; i++) {
        cin >> t[i];
        aLenyeg[i] = 0;
    }
}
void nagy() {
    for (int i = k; i <= n; i++) {
        int sum = 0;
        int maxx = t[i];
        int index = i;
        for (int j = i - 1; j >= i - k + 1; j--) {
            if (maxx <= t[j]) {
                maxx = t[j];
                index = j;
            }
        }
        for (int j = i; j >= i - k + 1; j--) {
            sum += abs(maxx - t[j] - (j - index));
        }
        aLenyeg[i] = sum;
    }

}

int main()
{
    be();
    nagy();
    int maxx = t[k];
    for (int i = k; i <= n; i++) {
        if (maxx > aLenyeg[i]) {
            maxx = aLenyeg[i];
        }
    }
    cout << maxx;
}