#include <bits/stdc++.h>
using namespace std;
 
int main() {
	long long N, M, A[100001];
	while(cin >> N >> M) {
		long long total = 0;
		for(int i = 0; i < N; i++) {
			cin >> A[i];
			total += A[i];
		}
		if(total < M) {
			cout << -1 << endl;
			continue;
		}
		sort(A, A+M, greater<int>());
		int lo = 0, hi = 1000000, mid;
		while(hi > lo) {
			mid = (lo+hi+1)/2;
			// cout << lo << " " << mid << " " << hi << " ";
			long long kayu = 0LL;
			for(int i = 0; i < N; i++)
				if(mid <= A[i])
					kayu += A[i]-mid;
			// cout << kayu << endl;
			if(kayu >= M)
				lo = mid;
			else
				hi = mid-1;
		}
		cout << lo << endl;
	}
	return 0;
}
 
/*
potong(X) = banyak kayu yang didapat klo
            dipotong di ketinggian X
potong(X) > potong(X+1) (decreasing)
yang dicari adalah nilai X sedemikian sehingga:
potong(X) >= M && potong(X+1) < M
 
binser untuk nilai X
  cek dari masing2 pohon dapat berapa kayu, jumlahkan
  
O(log(Ai) * log(N))
  
*/

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10 25
4 2 9 9 5 3 6 7 2 10
5 5
2 7 2 9 5
5 25
2 7 2 9 5
5 125
2 7 2 9 5