Problem:
Score : 400 points

Problem Statement

There are N persons called Person 1 through Person N.

You are given M facts that "Person A_i and Person B_i are friends." The same fact may be given multiple times.

If X and Y are friends, and Y and Z are friends, then X and Z are also friends. There is no friendship that cannot be derived from the M given facts.

Takahashi the evil wants to divide the N persons into some number of groups so that every person has no friend in his/her group.

At least how many groups does he need to make?

Constraints

2 \leq N \leq 2\times 10^5

0 \leq M \leq 2\times 10^5

1\leq A_i,B_i\leq N

A_i \neq B_i

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
\vdots
A_M B_M

Output

Print the answer.

Sample Input 1

5 3
1 2
3 4
5 1

Sample Output 1

3

Dividing them into three groups such as \{1,3\}, \{2,4\}, and \{5\} achieves the goal.

Sample Input 2

4 10
1 2
2 1
1 2
2 1
1 2
1 3
1 4
2 3
2 4
3 4

Sample Output 2

4

Sample Input 3

10 4
3 1
4 1
5 9
2 6

Sample Output 3

3

Solution in Julia (1.4.0) (judge verdict: Runtime Error)

function main()
    N,M = reads(Int,Int)
    fris = Set{Int}[]
    np = zeros(Int, N)
    for i in 1:M
        a,b = reads(Int,Int)
        if np[a] != 0 && np[b] != 0
            bi,si = length(fris[np[a]]) > length(fris[np[b]]) ? (np[a], np[b]) : (np[b], np[a])
            union!(fris[bi], fris[si])
            for j in fris[si]
                np[j] = bi
            end
        elseif np[a] != 0
            push!(fris[np[a]], b)
            np[b] = np[a]
        elseif np[b] != 0
            push!(fris[np[b]], a)
            np[a] = np[b]
        else
            push!(fris, Set([a,b]))
            np[a] = length(fris)
            np[b] = length(fris)
        end
    end
    println(maximum(map(x -> length(x), fris)))
end

import Base.parse
import Base.StringVector

parse(::Type{String},  str::AbstractString) = str
isdelim(x::UInt8, xs::Set{UInt8}) = x in xs
const delimset = Set([0x0a, 0x20])

function myreaduntil(s::IO, delims::Set{UInt8})::Vector{UInt8}
    out = StringVector(0)
    c::UInt8 = 0x00
    while !eof(s)
        c = read(s, UInt8)
        !isdelim(c, delims) && break
    end
    push!(out, c)
    eof(s) && return out
    while !eof(s)
        c = read(s, UInt8)
        isdelim(c, delims) && break
        push!(out, c)
    end
    return out
end

function readword(io::IO = stdin, delims = delimset)::String
    word = myreaduntil(io, delims)
    i = length(word)
    if i == 0 || word[i] != 0x0a
        return String(word)
    elseif i < 2 || word[i-1] != 0x0d
        return String(resize!(word,i-1))
    else
        return String(resize!(word,i-2))
    end
end

pread(ty) = parse(ty, readword())

reads(tys...)::Tuple{tys...} = Tuple{tys...}(pread(ty) for ty in tys)

function readvec(tys::Tuple , len::Signed)::Tuple{map(x -> Vector{x},tys)...}
    rv = Tuple{map(x -> Vector{x},tys)...}(Vector{ty}(undef,len) for ty in tys)
    for i in 1:len
        for j in 1:length(tys)
            @inbounds rv[j][i] = pread(tys[j])
        end
    end
    rv
end

readvec(ty::Type, len::Signed)::Vector{ty} = @inbounds ty[pread(ty) for i in 1:len]

function readmat(ty::Type, s...)::Matrix{ty}
    v = Matrix{ty}(undef, s...)
    @inbounds for i in 1:s[1]
        v[i,:] = readvec(ty, s[2])
    end
    v
end

main()