Go: package main

import (
    "fmt"
    "bufio"
    "strconv"
    "os"
    "strings"
    "math"
)

var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func readLine() string {
    buf := make([]byte, 0, 1000000)
    for {
        l, p, e := rdr.ReadLine()
        if e != nil {
            panic(e)
        }
        buf = append(buf, l...)
        if !p {
            break
        }
    }
    return string(buf)
}

func toInt(str string) int  {
    n, _ := strconv.Atoi(str)
    return n
}

func abs(a int) int {
    return int(math.Abs(float64(a)))
}

func getPar(x int, parent[1000]int) int {
    if parent[x] == x {
        return x
    } else {
        parent[x] = getPar(parent[x], parent)
        return parent[x]
    }
}

func main() {
    nm := strings.Split(readLine(), " ")
    n := toInt(nm[0])
    m := toInt(nm[1])
    var parent [1000]int
    for i := 0;i < n; i++ {
        parent[i] = i
    }


    for i := 0; i < m; i++ {
        ab := strings.Split(readLine(), " ")
        pa := getPar(toInt(ab[0]) - 1, parent)
        pb := getPar(toInt(ab[1]) - 1, parent)
        parent[pb] = pa
    }

    cities := make(map[int]int)
    villageCnt := 0
    for i := 0;i < n; i ++ {
        pi := getPar(i, parent)
        if i != pi {
            cities[pi] = 1
        } else {
            villageCnt ++
        }
    }
    cityCnt := len(cities)
    fmt.Println(abs(cityCnt * 2 - villageCnt))
}

C++: #include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iterator>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
#include <fstream>
#include <iomanip>
#include <cassert>
//#include <utility>
//#include <memory>
//#include <functional>
//#include <deque>
//#include <cctype>
//#include <ctime>
//#include <numeric>
//#include <list>
//#include <iomanip>

//#if __cplusplus >= 201103L
//#include <array>
//#include <tuple>
//#include <initializer_list>
//#include <forward_list>
//
//#define cauto const auto&
//#else

//#endif

using namespace std;


typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()
#define DEBUG
#ifdef DEBUG
#define dump(x)  cout << #x << " = " << (x) << endl;
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#else
#define dump(x) 
#define debug(x) 
#endif

#define MOD 1000000007LL
#define EPS 1e-8
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
#define maxs(x,y) x=max(x,y)
#define mins(x,y) x=min(x,y)

class UF {
	public:
	static const int ufmax=100052;
	int ufpar[ufmax],ufrank[ufmax],ufcnt[ufmax];
	UF() { init();}
	void init(){int i; rep(i,ufmax) { ufpar[i]=i; ufrank[i]=0; ufcnt[i]=1; } }
	int find(int x) {	return (ufpar[x]==x)?(x):(ufpar[x] = find(ufpar[x]));}
	int operator[](int x) {return find(x);}
	int count(int x) {return ufcnt[find(x)];}
	void unite(int x,int y) {
		x = find(x); y = find(y);
		if(x==y) return;
		if(ufrank[x]<ufrank[y]) ufpar[x]=y, ufcnt[y]+=ufcnt[x];
		else {ufpar[y]=x; ufcnt[x]+=ufcnt[y]; if(ufrank[x]==ufrank[y]) ufrank[x]++;}
	}
};



void mainmain(){
	int n,m;
	cin>>n>>m;
	UF uf;
	rep(i,m){
		int a,b;
		cin>>a>>b;
		a--;
		b--;
		uf.unite(a,b);
	}
	set<int> se;
	int a,b=0;
	rep(i,n){
		if(i==uf[i]) b++;
		else se.insert(uf[i]);
	}
	a=se.size();
	cout<<abs(a-b)<<endl;
	// cout<<abs((int)se.size()-(n-(int)se.size()))<<endl;
}


signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout<<fixed<<setprecision(20);
    mainmain();
}

C++: #include <iostream>
#include <map>
#include <algorithm>

#define rep(i, n) for(int i = 0; i < (n); ++i)

using namespace std;

int n, m;
int u[1000];

int find(int i){
  return u[i] == i ? i : u[i] = find(u[i]);
}
void unite(int a, int b){
  u[find(a)] = find(b);
}

int main(){
  cin >> n >> m;
  rep(i, n){
    u[i] = i;
  }
  rep(i, m){
    int a, b;
    cin >> a >> b;
    unite(a - 1, b - 1);
  }
  map<int, int> x;
  rep(i, n){
    ++x[find(i)];
  }
  int p = 0;
  for(auto& v: x){
    if(v.second > 1){
      ++p;
    }
    else{
      --p;
    }
  }
  cout << abs(p) << endl;
  return 0;
}

C++: #include<bits/stdc++.h>
#define LL long long
#define rep(i,n) for(int i=0;i<n;++i)
#define FOR(i,a,b) for(int i=a;i<=b;++i)
using namespace std;
static const LL INF = 1LL<<61LL;
static const int MAX_N = 10000;
typedef pair<int,int> PII;

PII P[MAX_N];
int par[MAX_N];
int rank[MAX_N];
int city[MAX_N];
int t[MAX_N];
int temp[MAX_N];
int n,m;
int ans;

class UF{
    public:
        void init(int n){
            rep(i,n){
                par[i]=i;
                rank[i]=0;
            }
        }

        int find(int x){
            if(par[x]==x){
                return x;
            }
            return par[x]=find(par[x]);
        }
        void unite(int x,int y){
            x=find(x);
            y=find(y);
            if(x==y)return;
            if(rank[x]<rank[y])par[x]=y;
            else {
                par[y]=x;
                if(rank[x]==rank[y])rank[x]++;
            }
        }

        bool same(int x,int y){
            return (find(x)==find(y));
        }
};

int main(){
    cin>>n>>m;
    UF uf;
    int V=n;
    uf.init(n);
    rep(i,m){
        int a,b;
        cin>>a>>b;
        if(!t[a])V--;
        if(!t[b])V--;
        t[a]=t[b]=1;
        uf.unite(a,b);
    }
    int val=0;
    rep(i,n+1){
        if(t[i])temp[uf.find(i)]=1;
    }
    rep(i,n+1){
        if(temp[i])val++;
    }
    ans=abs(val-V);
    cout<<ans<<endl;
}