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#include <bits/stdc++.h>
using namespace std;
using LL = long long;
#define e1 first
#define e2 second
#define pb push_back
#define OUT(x) {cout << x << "\n"; exit(0); }
#define TCOUT(x) {cout << x << "\n"; return; }
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define rep(i, l, r) for(int i = (l); i < (r); ++i)
#define boost {ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); }
#define sz(x) int(x.size())
#define trav(a, x) for(auto& a : x)
#define all(x) begin(x), end(x)
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
/*#include <atcoder/modint>
using namespace atcoder;
using mint = modint998244353;
vector <mint> fac, inv;
mint binom(int n, int k) {
	if (n < k || n < 0) return 0;
	return fac[n] * inv[k] * inv[n-k];
}

void prep(int N) {
	fac.resize(N+1, 1); inv.resize(N+1, 1);
	for (int i=1; i<=N; ++i) fac[i] = fac[i-1] * i;
	inv[N] = fac[N].inv();
	for (int i=N-1; i>0; --i) inv[i] = inv[i+1] * (i + 1);
}*/

mt19937_64 rng(time(0));
int random(int l, int r) {
	return uniform_int_distribution<int>(l, r)(rng);
}
#ifdef DEBUG
template<class T> int size(T &&x) {
	return int(x.size());
}
template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) {
	return out << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) {
	out << '{';
	for(auto it = x.begin(); it != x.end(); ++it)
		out << *it << (it == prev(x.end()) ? "" : ", ");
	return out << '}';
}
void dump() {}
template<class T, class... Args> void dump(T &&x, Args... args) {
	cerr << x << ";  ";
	dump(args...);
}
#endif
#ifdef DEBUG
  struct Nl{~Nl(){cerr << '\n';}};
# define debug(x...) cerr << (strcmp(#x, "") ? #x ":  " : ""), dump(x), Nl(), cerr << ""
#else
# define debug(...) 0 && cerr
#endif
const int maxn = 1000100;

//Did you REAALLY consider sample tests?

bool ok(vi vec, int k) {
	sort(vec.begin(), vec.begin() + k);
	for (int i=1; i<k; ++i) {
		if (vec[i] == vec[i-1]) return false;
	}
	return true;
}

ll brut(vi vec, int k) {
	int n = sz(vec);
	map <vi, int> dist;
	
	dist[vec] = 0;
	queue<vi> q;
	q.push(vec);
	
	while (!q.empty()) {
		vi fro = q.front();
		q.pop();
		if (ok(fro, k)) return dist[fro];
		for (int i=1; i<n; ++i) {
			vi cop = fro;
			swap(cop[i], cop[i-1]);
			if (dist.find(cop) == dist.end()) {
				dist[cop] = dist[fro] + 1;
				q.push(cop);
			}
		}
	}
	
	return -1;
}

ll wzo(vi vec, int k) {
	int n = sz(vec);
	vi jest(n + 1, 0);
	int curr = 0;
	
	ll res = 0;
	rep(i, 0, n) {
		if (curr == k) return res;
		if (!jest[vec[i]]) {
			res += i - curr;
			++curr;
		}
		
		jest[vec[i]] = 1;
	}
	
	if (curr >= k) return res;
	return -1;
}

bool TEST = 0;

int main() {
	boost;
	if (!TEST) {
		int n, k;
		cin >> n >> k;
		vi vec(n);
		rep(i, 0, n) cin >> vec[i];
		cout << wzo(vec, k) << "\n";
	}
	else {
		int testcount;
		cin >> testcount;
		FOR(_z, 1, testcount) {
			if (_z % 10 == 0) cout << "OK: " << _z << "\n";
			//TEST GENERATION
			int n = random(1, 8);
			int k = random(1, n);
			
			vi vec(n);
			rep(i, 0, n) vec[i] = random(1, n);
			//END TEST GENERATION
			auto model = wzo(vec, k);
			auto slow = brut(vec, k);
			if (model != slow) {
				debug(vec);
				debug(k);
				debug(model);
				debug(slow);
				OUT("WA");
			}
		}
	}
}