#include <bits/stdc++.h>


using namespace std;


long long solve(int n, int k, const vector <int> &arr) {
    vector <bool> seen(n, false);

    int numSeen = 0;
    long long ans = 0;

    for (int i = 0; i < n; i++) if (!seen[arr[i]]) {
        seen[arr[i]] = true;

        ans += i - numSeen;
        numSeen++;

        if (numSeen == k) {
            return ans;
        }
    }

    return -1;
}

int main() {
    ios_base::sync_with_stdio(false);

    int n, k;
    cin >> n >> k;

    vector <int> arr(n);
    for (int &ai : arr) {
        cin >> ai; ai--;
    }

    cout << solve(n, k, arr);

    return 0;
}