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#include <bits/stdc++.h>
#pragma GCC optimize(0fast)
#define BOOST ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define st first
#define nd second
#define pb push_back
#define INF 1000000000
#define mil 1000000
#define modulo 1000000007
using namespace std;
typedef long long ll;

using namespace std;
int tab[1000001];
int lic[1000001];
ll f(int n, int k){
	int it = 0, nr = -1;
	for(int i=0;i<n; i++){
		if(!lic[tab[i]]){
			it++;
		}
		lic[tab[i]]++;
		if(it == k){
			nr = i;
			break;
		}
	}
	if(nr == -1)
		return nr;
	ll res = 0;
	int x = 0;
	for(int i=nr; i>=0; i--){
		if(lic[tab[i]] > 1){
			res += (nr - i - x);
			lic[tab[i]]--;
			x++;
		}
	}
	return res;
}
int main(){
	BOOST;
	int n,k; cin >> n >> k;
	for(int i=0; i<n; i++){
		cin >> tab[i];
	}
	cout << f(n,k) << "\n";
}