bfs

type
  triplet = record
    u, pr, v: integer;
  end;

var
  list, head, next, a, b, vv: array [1..2500000] of integer;
  joo: array [0..9000000] of triplet;
  i, h, f, m, n, u, uu, ish, beg, en: integer;

procedure push(a, b: integer);
begin
  inc(h);
  list[h] := b;
  next[h] := head[a];
  head[a] := h;
end;

procedure push1(u, pr, v: integer);
begin
  en := (en + 1) mod 9000000;
  joo[en].u := u;
  joo[en].pr := pr;
  joo[en].v := v;
end;

function min(a, b: integer): integer;
begin
  if a < b then min := a
  else min := b;
end;

procedure bfs();
var
  u, pr, v: integer;
begin
  while (beg <> en) do
  begin
    beg := (beg + 1) mod 9000000;
    u := joo[beg].u;
    pr := joo[beg].pr;
    v := joo[beg].v;
    b[u] := pr;
    vv[u] := v;
    u := head[u];
    while (u <> 0) and ((v + 1) * 2 + 1 < f) do
    begin
      if (b[list[u]] <> pr) and (b[list[u]] <> 0) then f := min(f, v + 1 + vv[list[u]])
      else if (b[list[u]] = 0) then push1(list[u], pr, v + 1);
      u := next[u];
    end;
  end;
end;

begin
  readln(n, m);
  h := 0;
  beg := 0;
  en := 0;
  for i := 1 to n do read(a[i]);
  for i := 1 to m do
  begin
    readln(u, uu);
    push(u, uu);
    push(uu, u);
  end;
  f := m + 2;
  for ish := 1 to n do
    if (a[ish] <> 0) then
      push1(ish, a[ish], 0);
  bfs;
  writeln(f);
end.