type trec = record
     kota, wkt : longint;
     tol : boolean;
end;

var
  qh, qt : longint;
  q : array [1..125000] of trec;
  lewat : array [1..500] of byte;

procedure init;
begin
  qh := 0;
  qt := 0;
end;

procedure insert (d : trec);
begin
  if qh = 0 then qh := 1;
  inc (qt);
  q[qt] := d;
end;

function delete : trec;
var hasil : trec;
begin
  hasil := q[qh];
  if qh = qt then init else inc (qh);
  delete := hasil;
end;


var
  jumkota, jumjalan, jumtol, awal, roma, b, k, a, ja, jb : longint;
  s, s1, s2 : trec;
  ketemu : boolean;
  mat, mattol : array [1..500, 1..500] of longint;
begin
  qh:=0;
  qt:=0;
  readln (jumkota, jumjalan, jumtol, awal, roma);
  for b := 1 to jumkota do begin
    for k := 1 to jumkota do begin
      mat[b,k] := 0;
      mattol[b,k] := 0;
    end;
  end;

  for a := 1 to jumjalan do begin
    readln (ja, jb);
    mat[ja, jb] := 1;
    mat[jb, ja] := 1;
  end;

  for a := 1 to jumtol do begin
    readln (ja, jb);
    mattol[ja, jb] := 2;
    mattol[jb, ja] := 2;
  end;

  {for b:= 1 to jumkota do begin
    for k:= 1 to jumkota do
      write(mat[b,k]:4);
    writeln;
  end;}


  ketemu := false;
  s.tol := false;
  s.wkt := 0;
  s.kota := awal;
  for a := 1 to 500 do begin
    lewat[a] := 0;
  end;
  lewat[awal] := 1;
  insert (s);

  while (ketemu = false) and ((qh <> 0) and (qt <> 0)) do begin
    s1 := delete;
    //write('kota skr=',s1.kota);
    //if s1.tol=true then write(' sudah tol ') else write(' belum tol ');
    //writeln('jarak=',s1.wkt);
    if s1.kota = roma then ketemu := true else begin
      s2.wkt:= s1.wkt + 1;
      for k := 1 to jumkota do begin
        if (mat[s1.kota, k] = 1) and ((lewat[k] = 0) or (lewat[k] = 2))
        then begin
          lewat[k] := 1;
          s2.tol := false;
          //cektol[k] := false;
          s2.kota := k;
          //writeln('expand ke=',s2.kota,' tanpa tol');
          insert (s2);
        end else if (mattol[s1.kota, k] = 2) and (lewat[k] = 0) and
        (s1.tol = false) then begin
          lewat[k] := 2;
          s2.tol := true;
          //cektol[k] := true;
          s2.kota := k;
          //writeln('expand ke=',s2.kota,' dengan tol');
          insert (s2);
        end;
      end;
    end;
  end;

  if ketemu = true then writeln (s1.wkt);
end.