// Homura Akemi a.k.a. Starrykiller (/user/235125)
// I love Madoka Kaname forever! 
#include <bits/stdc++.h>

using namespace std;

template<typename L, typename R>
auto range(L l, R r) { return views::iota(l,r); }
auto rev=views::reverse;

template<typename T>
_GLIBCXX_ALWAYS_INLINE void chmax(T &a, T b) { a=max(a,b); }
template<typename T>
_GLIBCXX_ALWAYS_INLINE void chmin(T &a, T b) { a=min(a,b); }
#define int long long

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
// int T; cin>>T;
int T=1;
while (T--) []{
    int n, k;
    cin>>n>>k;
    set<int> s; int cnt=0, ans=0;
    for (auto _: range(0,n)) {
        int x; cin>>x;
        if (s.insert(x).second) ans+=cnt;
        else cnt++;
        if ((int)size(s)==k) {
            cout<<ans; return;
        }
    }
    cout<<"-1";
}();
}