#include <stdio.h>
#define Nmax 20000
int x,cnt=0,viz[Nmax],y,m,n,A[Nmax][Nmax];
void DFS(int q)
{int i;
     viz[q]=1;
     for(i=1;i<=A[q][0];i++)
       if(!viz[i])
       {
        cnt++;
        DFS(A[q][i]);
       }
}        
int main()
{int i;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
    for(i=1;i<=m;i++)
      {
        scanf("%d %d",&x,&y);
        A[x][0]++;A[x][A[x][0]]=y;
        A[y][0]++;A[y][A[y][0]]=x;
      }
    DFS(1);
    printf("%d\n",cnt);
    return 0;
}