#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define endl "\n"
#define pll pair<ll,ll>
#define fs first
#define sc second

const ll MOD = 1e9+7;

void solve()
{
    ll n, k;
    cin >> n >> k;
    vector<ll> a(n);
    
    for(ll i = 0; i < n; i++) cin >> a[i];
    
    if(k == 1)
    {
        cout << 0 << endl;
        return;
    }

    ll ans = LLONG_MAX-1;

    for(ll i = 0; i < n-k+1; i++)
    {
        ll maxe = a[i];
        ll maxl = 0;
        /*
        for(ll j = 0; j < k; j++)
        {
            if(a[i+j] >= maxe)
            {
                maxe = a[i+j];
                maxl = j;
            }
        }
        */

        ll ans2 = 0;
        
        for(ll j = 0; j < k; j++)
        {
            ll magas = maxl-j + maxe;
            ans2 += magas - a[i+j];
        }
        ans = min(ans, ans2);
    }
    cout << ans << endl;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    ll t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}