C++ :

#include<cstdio>
#include<queue>
using namespace std;
int s,n,m,f[101],d[101];
queue<int>q;
int main()
{
	int i,a,b,fa,fb;
	while(~scanf("%d%d",&n,&m))
	{
		for(i=1;i<=n;i++)
			f[i]=i,d[i]&=0;
		for(i=0;i<m;i++)
		{
			scanf("%d%d",&a,&b);
			f[b]=a;
		}
		for(s=0,i=1;i<=n;i++)
			if(i==f[i])
				s++,q.push(i);
			printf("%d\n%d",s,q.front());
			q.pop();
			while(!q.empty())
				printf(" %d",q.front()),q.pop();
	}
	return 0;
}

Pascal :

program qi26790;
var
 a:array[1..100]of longint;
 h,i,j,n,k,s:longint;
begin
 read(n,k);
 for i:= 1 to n do a[i]:=0;
 for i:= 1 to k do
  begin
   read(h,j);
   a[j]:=h;
  end;
  s:=0;
 for i:= 1 to n do
   if a[i]=0 then inc(s);
   writeln(s);
  for i:=1 to n do
   if a[i]=0 then write(i,' ');
end.