1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef pair<ld, ld> PLD;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef vector<PII> VII;
typedef vector<VI> VVI;
typedef vector<VL> VVL;
typedef vector<VII> VVII;
typedef vector<PLL> VLL;
typedef vector<VLL> VVLL;
typedef vector<VI> VVI;
typedef vector<VL> VVL;
typedef vector<bool> VB;

template <class T, class G>
ostream &operator<<(ostream &os, const pair<T, G> &para) {
  os << para.first << " " << para.second;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (const T &el : vec)
    os << el << " ";
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &vec) {
  for (const T &el : vec)
    os << el << " ";
  return os;
}

#define REP(i, j) for (int i = 0; i < j; i++)
#define REP1(i, j) for (int i = 1; i < j; i++)
#define FOREACH(el, n) for (auto &el : n)
#define LAST(x) (x[(int)x.size() - 1])
#define pb push_back
#define pf push_front
#define st first
#define nd second
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sp ' '
#define ent '\n'

const int N = 600000;
const int M = 1e6;
const int INF = 1e6 - 5;
bitset<N> used;

struct FenwickTree {
  VL bit;
  int n;

  FenwickTree(int n) {
    this->n = n;
    bit.assign(n, 0);
  }

  ll sum(int r) {
    ll ret = 0;
    for (; r >= 0; r = (r & (r + 1)) - 1)
      ret += bit[r];
    return ret;
  }

  void add(int idx, ll delta) {
    for (; idx < n; idx = idx | (idx + 1))
      bit[idx] += delta;
  }
};

FenwickTree tr = FenwickTree(M);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);

  int t = 1;
  // cin >> t;
  while (t--) {
    ll n, k;
    cin >> n >> k;
    VL v;
    ll different = 0;
    ll ans = 0;
    REP(i, n) {
      ll a;
      cin >> a;
      if (!used[a] && different < k) {
        different++;
        used[a] = true;
        a = different;
      } else {
        a = INF;
      }
      v.pb(a);
    }
    if (different < k) {
      cout << -1 << ent;
      return 0;
    }
    for (ll i = 0; i < (ll)v.size(); i++) {
      ans += (ll)(i - tr.sum(v[i]));
      tr.add(v[i], 1);
    }
    cout << ans;
  }

  return 0;
}