program task_d;

{$APPTYPE CONSOLE}

uses
  SysUtils;
  type list= array of longint;
var
f:text;
a:array[1..100000] of list;
n,m,i,j,st:longint;
x,y,l:array[1..100000] of longint;
visited:array[1..100000] of boolean;
error:boolean;

procedure connect(v:longint);
var
i:longint;
begin
visited[v]:=false;
for i:=1 to l[v] do
begin
if (visited[a[v][i]]) then connect(a[v][i]);
end;
end;




begin
fillchar(l,sizeof(l),0);
assign(f,'penalty.in');
reset(f);
readln(f,n,m);
for i:=1 to m do
begin
readln(f,x[i],y[i]);
inc(l[x[i]]);
inc(l[y[i]]);
end;
for i:=1 to n do setlength(a[i],l[i]);
 fillchar(l,sizeof(l),0);
for i:=1 to m do
begin
inc(l[x[i]]);
a[x[i]][l[x[i]]]:=y[i];
inc(l[y[i]]);
a[y[i]][l[y[i]]]:=x[i];
end;
readln(f,st);
close(f);
connect(st);
error:=false;
fillchar(visited,sizeof(visited),true);
if (visited[1]) then error:=true;

assign(f,'penalty.out');
rewrite(f);
if (error) then writeln(f,-1) else writeln(f,0);
close(f);

fillchar(a,sizeof(a),0);
  { TODO -oUser -cConsole Main : Insert code here }
end.