var
      i,n,m,cnt,x,y,s,f : longint;
      v,pred : array [1..100000] of longint;
      u      : array [1..1000] of longint;

      function bfs(x,f : longint) : longint;
      var
        qb,qe,sn : longint;
        q : array [1..10000,1..2] of longint;
        was : array [1..1000] of boolean;
      begin
        fillchar(was,sizeof(was),false);
        fillchar(q,sizeof(q),0);
        qb:=1;
        qe:=0;
        inc(qe);
        q[qe,1]:=x;
        q[qe,2]:=0;
        was[x]:=true;
        while (qe>=qb) do begin
          x:=q[qb,1];
          sn:=q[qb,2];
          inc(qb);
          inc(sn);
          x:=u[x];
          while (x<>0) do begin
            if (not was[v[x]])
              then begin
                if (v[x]=f)
                  then begin
                    bfs:=sn;
                    exit;
                  end;
                inc(qe);
                q[qe,1]:=v[x];
                q[qe,2]:=sn;
                was[v[x]]:=true;
              end;
            x:=pred[x];
          end;
        end
      end;


      procedure add(x,y : longint);
      begin
        inc(cnt);
        v[cnt]:=y;
        pred[cnt]:=u[x];
        u[x]:=cnt;
      end;

    begin
      assign(input,'input.txt'); reset(input);
      assign(output,'output.txt'); rewrite(output);
      readln(n,m);
      for i:=1 to m do begin
        readln(x,y);
        add(x,y);
        add(y,x);
      end;
      readln(s,f);
      writeln(bfs(s,f));
      close(input); close(output);
    end.