C++ :

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<string>
#include<queue>
#define s1 100002
#define s2 200002
#define s3 30005
using namespace std;
struct  node
{
	int y;
	int next;
}e[s2];
int tot=0;
int g[s3]={0};
bool b[s3]={0};

void jian(int x,int y)
{
	e[++tot].y=y;
	e[tot].next=g[x];
	g[x]=tot;
}

int main()
{
	//freopen("damage.in","r",stdin);
	//freopen("damage.out","w",stdout);
	int n,p,c;
    cin>>p>>c>>n;
    
    int x,y,m;
    queue <int> q;
   
	for(int i=1;i<=c;i++)
	{
		cin>>x>>y;
		jian(x,y);
		jian(y,x);
	}
	
	for(int i=1;i<=n;i++)
	{
		cin>>m;
		q.push(m); 
		b[m]=1;
		int pos=g[m];
		while(pos!=0)
		{
			b[e[pos].y]=1;	
			pos=e[pos].next;
		}	
		
   }
		
	q.push(1);
	b[1]=1;
	int sum=1;
	while(!q.empty())
	{
		    int f=q.front();
			int pos=g[f];
			while(pos!=0)
			{
				if(!b[e[pos].y])
				{
					q.push(e[pos].y);
					b[e[pos].y]=1;
		            sum++;
				}
				pos=e[pos].next;
			}
			q.pop();
	}
	cout<<p-sum;
	return 0;
}

Pascal :

type
  ji=^rec;
  rec=record
  data:longint;
  next:ji;
end;
var
  a:array[0..30001] of ji;
  q:array[0..30001] of longint;
  v:array[0..30001] of boolean;
  head,tail,n,m,p,i,j,k,ans:longint;
  pp:ji;
 
procedure insert(x,y:longint);
var
  p:ji;
begin
  new(p); p^.data:=y; p^.next:=a[x]; a[x]:=p;
  new(p); p^.data:=x; p^.next:=a[y]; a[y]:=p;
end;
 
procedure dfs(x:longint);
var
  p:ji;
begin
  v[x]:=true;
  dec(ans);
  p:=a[x];
  while p<>nil do
    begin
      if not v[p^.data] then dfs(p^.data);
      p:=p^.next;
    end;
end;
 
procedure cannot(x:longint);
var
  p:ji;
begin
  p:=a[x];
  v[x]:=true;
  while p<>nil do
    begin
      v[p^.data]:=true;
      p:=p^.next;
    end;
end;
 
begin
  
  readln(n,m,p);
  for i:=1 to m do
    begin
      readln(j,k);
      if j=k  then continue;
      insert(j,k);
    end;
  for i:=1 to p do
    begin
      readln(k);
      cannot(k);
    end;
  ans:=n-1;
  head:=1; tail:=1; q[1]:=1; v[1]:=true;
  while head<=tail do
    begin
      pp:=a[q[head]];
      while pp<>nil do
        begin
          if not v[pp^.data] then
            begin
              v[pp^.data]:=true;
              dec(ans);
              inc(tail);
              q[tail]:=pp^.data;
            end;
          pp:=pp^.next;
        end;
      inc(head);
    end;
  writeln(ans);
  
end.