#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 2e6 + 9;
int n,ans;
int a[N],min_a,max_a;
int c[N];
int K;
struct BinaryIndexedTree{
	int t[N];
	int lowbit(int x){
		return x & (-x);
	}
	void update(int pos,int v){
		if(pos <= 0)
			return;
		for(int i = pos;i <= n;i += lowbit(i))
			t[i] += v;
	}
	int query(int pos){
		if(pos <= 0)
			return 0;
		int ret = 0;
		for(int i = pos;i;i -= lowbit(i))
			ret += t[i];
		return ret;
	}
	void clear(int pos){
		if(pos <= 0)
			return;
		for(int i = pos;i <= n;i += lowbit(i))
			t[i] = 0;
	}
} BIT;
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	cin >> n >> K;
	ans = n;
	min_a = LLONG_MAX;
	for(int i = 1;i <= n;i++){
		cin >> a[i];
		min_a = min(min_a,a[i]);
		max_a = max(max_a,a[i]);
	}
	if(min_a == max_a){
		cout << -1;
		return 0;
	}
	int l = 1,r = 1;
	int tmp = 0;
	for(;l <= n;l++){
		for(;r <= n && tmp < K;r++){
			BIT.update(c[a[r]],-1);
			c[a[r]]++;
			BIT.update(c[a[r]],1);
			tmp += 1ll * (BIT.query(n) - BIT.query(c[a[r]] - 1) - 1);
		}
		if(r > n)
			break;
		ans = min(ans,r - l);
		BIT.update(c[a[l]],-1);
		c[a[l]]--;
		BIT.update(c[a[l]],1);
		tmp -= 1ll * (BIT.query(n) - BIT.query(c[a[l]]));
	}
	cout << ans;
	return 0;
}