1118D.cpp

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;
typedef long long ll;

struct int_hash {
    static uint64_t splitmix64(uint64_t x) {
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};

struct pair_hash {
    size_t operator()(pair<int, int> x) const {
        return int_hash{}(x.first) ^ (int_hash{}(x.second) << 16);
    }
};

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int MOD = 1000000007;
const ll INF = numeric_limits<ll>::max();
const int inf = 1e7;
const int MX = 100001; //check the limits, dummy

bool check(const vector<ll> &v, const ll buckets, const ll m) {
    ll sum = 0;
    for(ll i = 0; i < v.size(); i++)
        sum += max(0LL, v[i] - i/buckets);
    return sum >= m;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    
    ll n, m; cin >> n >> m;
    vector<ll> v(n);
    for(ll&i : v) cin >> i;

    ll sum = accumulate(begin(v), end(v), 0LL);
    if(sum < m)
        cout << -1 << endl;
    else {
        sort(rbegin(v), rend(v));
        ll lo = 0, hi = n;
        while(hi - lo > 1) {
            ll mid = (hi - lo) / 2 + lo;
            if(check(v, mid, m)) hi = mid;
            else lo = mid;
        }
        cout << hi << endl;
    }
}