// Wiktor Onik 2021
#include <bits/stdc++.h>

using namespace std;
map<int, int> m;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int n, k, li = 0, licz = 0, wyn = 0, mi = 0;
    cin >> n >> k;
    int tab[n + 9];

    for (int i = 0; i < n; i++)
    {
        cin >> tab[i];
    }

    for (int i = 0; i < n; i++)
    {
        if (m.count(tab[i]) == 0)
        {
            m[tab[i]] = 1;

            licz++;
            wyn += i - mi;
            mi++;
        }
        if (licz == k)
        {
            cout << wyn << endl;
            return 0;
        }
    }

    cout << -1 << endl;
    return 0;
}