private class Node{
		HashSet<Integer> fromThis;  //this -> neighbours
		HashSet<Integer> toThis;    //neighbours -> this
		LinkedList<Integer> neighbours; //all vertexes from this
		Node(){
			fromThis=new HashSet<Integer>();
			toThis=new HashSet<Integer>();
			neighbours=new LinkedList<Integer>();
		}
	}

	private class Graph{
		private BufferedReader in;
		private PrintWriter out;
		private StringTokenizer st;
		private Stack<Integer> stack;
		private int colors[];
		private int timeOfDeath[];
		private HashSet<Integer> doesntUsed;

		private int vNum;   //number of vertexes
		private int eNum;	//number of edges
		private Node gr[];


		Graph(){
			vNum=0;
			eNum=0;
		}
		Graph(String arg)throws IOException{
			loadGraph(arg);
		}

		public boolean isEmpty(){
			return vNum==0;
		}
		private void addEdge(int a, int b){  //from a to b
			gr[a-1].fromThis.add(b);
			gr[b-1].fromThis.add(a);
			gr[a-1].neighbours.add(b);
			eNum++;
		}

		public void loadGraph(String arg)throws IOException{
			in=new BufferedReader(new FileReader(arg));
			String temp=in.readLine();
			st=new StringTokenizer(temp);
			vNum=Integer.parseInt(st.nextToken());
			int e=Integer.parseInt(st.nextToken());
			gr=new Node[vNum];
			int i;
			for (i=0; i<vNum; i++){
				gr[i] = new Node();
			}
			if (e>0){
				int a,b;
				for (i=0; i<e; i++){
					temp=in.readLine();
					st=new StringTokenizer(temp);
					a=Integer.parseInt(st.nextToken());
					b=Integer.parseInt(st.nextToken());
					addEdge(a, b);
				}
			}
			in.close();
		}
		public boolean topSort(int a){    //a- вершина с которой начинается...
			stack=new Stack<Integer>();
			colors=new int[vNum];
			doesntUsed=new HashSet<Integer>();
			timeOfDeath=new int[vNum];
			int i, index=a, temp;
			for (i=0; i<vNum; i++){
				colors[i]=0;
				doesntUsed.add(i+1);
			}
			stack.push(index);
			colors[a-1]=1;
			while (!(doesntUsed.isEmpty())){
				doesntUsed.remove(index);
				for (i=1; i<gr[index-1].neighbours.size()+1; i++){
					temp=gr[index-1].neighbours.get(i);
					if (colors[temp-1]==0){
						stack.push(temp);
						colors[temp-1]=1;
						//еще не были тут.
					} else {
						if (!doesntUsed.contains(temp)){
							return false;
							//цикл
						}else{
							//нет цикла, но тут были уже
						}
					}
				}
				index=stack.lastElement();
			}
			i=0;
			while (!(stack.isEmpty())){
				timeOfDeath[i]=stack.pop();
				i++;
			}
			return true;
		}
	}