#include <bits/stdc++.h>
//#pragma GCC optimize("O3")
#define count masloriy1489
#define y1 jhgfds
#define ll long long
#define pb push_back
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for(ll i = 0; i < n; i++)

using namespace std;
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

int main(){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    #define int long long
    int n, m;
    cin >> n >> m;
    vector<int> a(n);
    int sum = 0;
    rep(i, n){
        cin >> a[i];
        sum += a[i];
    }
    if(sum < m){
        cout << -1;
        return 0;
    }
    sort(all(a));
    int l = 1, r = n;
    while(r - l > 1){
        int c = (l + r)>>1;
        vector<int> b(a);
        int now = m;
        int diff = 0;
        while(!b.empty() && now > 0){
            rep(i, c){
                if(b.empty())
                    break;
                now = now - (b.back()-diff);
                b.pop_back();
            }
            diff++;
        }
        if(now <= 0)
            r = c;
        else
            l = c;
    }
    int c = l;
    vector<int> b(a);
    int now = m;
    int diff = 0;
    while(!b.empty() && now > 0){
        rep(i, c){
            if(b.empty())
                break;
            now -= (b.back()-diff);
            b.pop_back();
        }
        diff++;
    }
    if(now <= 0)
        c = l;
    else
        c = r;
    cout << c;
}