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.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Runtime.Remoting.Messaging;
using System.Security.Principal;
using System.Text;
class Simple {
    private long N, A, B;
    private long[] h;
    void Solve() {
        //input
        N = io.Int;
        A = io.Int;
        B = io.Int;
        h=new long[N];
        for(int i = 0; i < N; ++i) h[i] = io.Int;
        //cal
        var diff = A - B;
        Func <long, bool> isOK = (num) => {
            var damaged = B * num;
            var addNum = 0L;
            for(int i = 0; i < N; ++i) {
                var left = h[i] - damaged;
                if(left > 0) addNum += left / diff + (left % diff == 0 ? 0 : 1);
            }            
            return addNum<=num;
        };
        var ans = binarySearch(h, -1, (long)1e9 + 5, isOK);
        //ret
        Console.WriteLine(ans);            
    }

    long binarySearch(long[] a, long ng, long ok, Func <long, bool> check) {
        while(ok - ng > 1) {
            long mid = (ok + ng) / 2;
            if(check(mid)) ok = mid;
            else ng = mid;
        }
        return ok;
    }
    
    SimpleIO io = new SimpleIO();
    public static void Main(string[] args) => new Simple().Stream();
    void Stream() {
        Solve();
        io.writeFlush();
    }
}
class SimpleIO {
    string[] nextBuffer;
    int BufferCnt;
    char[] cs = new char[] {' '};
    StreamWriter sw = new StreamWriter(Console.OpenStandardOutput()) {AutoFlush = false};
    public SimpleIO() {
        nextBuffer = new string[0];
        BufferCnt = 0;
        Console.SetOut(sw);
    }
    public string Next() {
        if(BufferCnt < nextBuffer.Length) return nextBuffer[BufferCnt++];
        string st = Console.ReadLine();
        while(st == "") st = Console.ReadLine();
        nextBuffer = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
        BufferCnt = 0;
        return nextBuffer[BufferCnt++];
    }
    public string String => Next();
    public char Char => char.Parse(String);
    public int Int => int.Parse(String);
    public long Long => long.Parse(String);
    public double Double => double.Parse(String);
    public void writeFlush() { Console.Out.Flush(); }
}