{$A8,B-,C+,D+,E-,F-,G+,H+,I+,J-,K-,L+,M-,N+,O-,P+,Q-,R-,S-,T-,U-,V+,W-,X+,Y+,Z1}
program z1320;

{$APPTYPE CONSOLE}

uses
  SysUtils;
type
  pnode = ^tnode;
  tnode = record
    b:longint;
    next:pnode;
  end;
var a:array [1..1000] of pnode;
    c:array [1..1000] of longint;
    b:array [1..1000] of boolean;
    n,m,i,j,k,t:longint;
    x:pnode;
procedure init;
begin
  reset(input,'input.txt');
  rewrite(output,'output.txt');
end;
procedure print;
begin
  close(input);
  close(Output);
  halt(0);
end;
procedure swap(var a,b:longint);
var t:longint;
begin
 t:=a;
 a:=b;
 b:=t;
end;
procedure dfs(k:longint);
begin
  b[k]:=true;
  inc(c[m]);
  while a[k]<>nil do
    begin
     if b[a[k]^.b]=false then
      dfs(a[k]^.b);
     a[k]:= a[k]^.next;
    end;
end;
begin
  init;
  n:=0;
  while not seekeof(input) do
   begin
     read(i,j);
     new(x);
     x^.b:=j;
     x^.next:=a[i];
     a[i]:=x;
     new(x);
     x^.b:=i;
     x^.next:=a[j];
     a[j]:=x;
     if i<j then swap(i,j);
     if i>n then n:=i;
   end;
  m:=0;
  for i:=1 to n do
    if b[i]=false then
      begin
       inc(m);
       dfs(i);
      end;
  for i:=1 to m do
   if c[i]=2 then
    begin
     write(0);
     halt(0);
    end;
  write(1);
  print;
end.