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#include <bits/stdc++.h>

using namespace std;

#define ALL(x) (x).begin(), (x).end()

template<class C> void mini(C &a5, C b5) { a5 = min(a5, b5); }
template<class C> void maxi(C &a5, C b5) { a5 = max(a5, b5); }

#ifdef LOCAL
const bool debug = true;
#else
const bool debug = false;
#define cerr if (true) {} else cout
#endif

#define int long long
#define double long double

const int INF = 1e18;
const int mod = 1e9 + 7;

const int nax = 1000010;

bool is_present[nax];
int ones_count;
int res;

int32_t main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    
    int n, k;
    cin >> n >> k;
    
    for (int i = 1; i <= n; i++) {
		int a;
		cin >> a;

		if (!is_present[a]) { // 0
			res += ones_count;
		} else { // 1
			ones_count++;
		}

		is_present[a] = true;
		
		if (i - ones_count == k) { // there is k zeros
			cout << res << "\n";
			return 0;
		}
	}
	
	cout << "-1\n";
    
    return 0;
}/*
5 3
3 3 3 1 2

3 2
1 1 1
*/