Problem:
Score : 400 points

Problem Statement

You are going out for a walk, when you suddenly encounter N monsters. Each monster has a parameter called health, and the health of the i-th monster is h_i at the moment of encounter. A monster will vanish immediately when its health drops to 0 or below.

Fortunately, you are a skilled magician, capable of causing explosions that damage monsters. In one explosion, you can damage monsters as follows:

Select an alive monster, and cause an explosion centered at that monster. The health of the monster at the center of the explosion will decrease by A, and the health of each of the other monsters will decrease by B. Here, A and B are predetermined parameters, and A > B holds.

At least how many explosions do you need to cause in order to vanish all the monsters?

Constraints

All input values are integers.

1 ≤ N ≤ 10^5

1 ≤ B < A ≤ 10^9

1 ≤ h_i ≤ 10^9

Input

Input is given from Standard Input in the following format:

N A B
h_1
h_2
:
h_N

Output

Print the minimum number of explosions that needs to be caused in order to vanish all the monsters.

Sample Input 1

4 5 3
8
7
4
2

Sample Output 1

2

You can vanish all the monsters in two explosion, as follows:

First, cause an explosion centered at the monster with 8 health. The healths of the four monsters become 3, 4, 1 and -1, respectively, and the last monster vanishes.

Second, cause an explosion centered at the monster with 4 health remaining. The healths of the three remaining monsters become 0, -1 and -2, respectively, and all the monsters are now vanished.

Sample Input 2

2 10 4
20
20

Sample Output 2

4

You need to cause two explosions centered at each monster, for a total of four.

Sample Input 3

5 2 1
900000000
900000000
1000000000
1000000000
1000000000

Sample Output 3

800000000

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            ARC075.D();
        }
        class ARC075
        {
            public static void C()
            {
                var N = Read.Int();
                var S = Enumerable.Range(0, N).Select(i => Read.Int()).ToArray();
                var total = S.Sum();
                if (total % 10 > 0) { Console.WriteLine(total); return; }
                var min = 999;
                foreach(var s in S)
                {
                    if(s%10>0 && min > s) { min = s; }
                }
                Console.WriteLine(min == 999 ? 0 : total - min);
            }
            public static void D()
            {
                var N = Read.Int();
                var A = Read.Long();
                var B = Read.Long();
                var H = Enumerable.Range(0, N).Select(i => Read.Long()).ToArray();

                Func<long, bool> Win = K =>
                {
                    long need = 0;
                    foreach(var h in H)
                    {
                        if(h > K * B)
                        {
                            need += (h - K * B + A - B - 1) / (A - B);
                        }
                    }
                    return K >= need;
                };

                long min = 0;
                long max = (long)1e9;
                while (min + 1 < max)
                {
                    var mid = (min + max) / 2;
                    if (Win(mid))
                    {
                        max = mid;
                    }
                    else
                    {
                        min = mid;
                    }
                }
                Console.WriteLine(max);
            }
            public static void E()
            {
                var N = Read.Int();
                var K = Read.Long();
                var A = Enumerable.Range(0, N).Select(i => Read.Long()).ToArray();
                var comp = Util.Compress(Util.ASum(A).Select((x, i) => x - i * K).ToArray());
                var bit = new Util.BIT(N + 1);
                long ans = 0;
                for (int i = 0; i <= N; ++i)
                {
                    ans += bit.Sum(comp[i]);
                    bit.Add(comp[i], 1);
                }
                Console.WriteLine(ans);
            }
        }
        class Util
        {
            public static int[] Compress(long[] array, bool needDistinct = true)
            {
                var sorted = needDistinct ? array.Distinct().ToArray() : array.ToArray(); Array.Sort(sorted);
                Dictionary<long, int> dict = new Dictionary<long, int>(); for (int i = 0; i < sorted.Length; ++i) { dict.Add(sorted[i], i + 1); }
                return array.Select(x => dict[x]).ToArray();
            }
            public static long[] ASum(long[] array)
            {
                var res = new long[array.Length + 1];
                for (int i = 0; i < array.Length; ++i)
                {
                    res[i + 1] = res[i] + array[i];
                }
                return res;
            }
            public class BIT
            {
                int N; long[] array;
                public BIT(int m) { for (int n = 1; ; n *= 2) { if (n >= m) { N = n; array = new long[N + 1]; break; } } }
                public void Add(int idx, int v) { for (int x = idx; x <= N; x += x & -x) { array[x] += v; } }
                public long Sum(int idx) { long ret = 0; for (int x = idx; x > 0; x -= x & -x) { ret += array[x]; } return ret; }
            }
        }

        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static ulong[] ULongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToUInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M, bool isDirectional = false)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i) { dict.Add(i, new HashSet<int>()); }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN(); dict[ab[0]].Add(ab[1]);
                    if (!isDirectional) { dict[ab[1]].Add(ab[0]); }
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}