#include<iostream>

 #include<memory.h>

 #include<queue>

 using namespace std;

 bool roads[][];

 bool visited[];

 int N,M;

 int main(){

     cin >>N >>M;

     memset(roads,,sizeof(roads));

     memset(visited,false,sizeof(visited));

     int from,dest;

     for(int i=; i<=M; i++){

         cin >> from >> dest;

         roads[from][dest] = true;

         roads[dest][from] = true;

     }

     queue<int> check;

     int num = ;

     int cnt = ;

     int i;

     //breadth-frist search

     while(num != N){

         for( i=; i<=N;i++){

             if(visited[i]== false){

                 check.push(i);

                 visited[i]= true;

                 num++;

                 cnt++;

                 break;

             }

         }

         while(!check.empty()){

             i = check.front();

             for(int j = ; j<=N;j++){

                 if(roads[i][j] == true && visited[j] == false){

                     check.push(j);

                     visited[j] = true;

                     num++;

                 }

             }

             // erase the front node

             check.pop();

         }

     }

     cout << cnt <<endl;

     return ;

 }