program Project2;

{$APPTYPE CONSOLE}

uses
  SysUtils, Math;

const
  MAXIN = 1000000;

type
  time = record
    data, prev, st: integer;
    ans: int64;
  end;

var
  z, n, m, i, j, x, y, data, ind, free, h, p, last, min1, min2: integer;
  a, mark, s, head, dest, next, ans, ans1: array [0..MAXIN] of integer;
  q: array [0..MAXIN] of time;
  bol: boolean;

function size(p, last: integer): boolean;
begin
  size := (p <= last) or (last > p);
end;

procedure add(v, u: integer);
begin
  inc(free);
  dest[free] := u;
  next[free] := head[v];
  head[v] := free;
end;

begin
  min2 := MAXINT - 20;
  last := -1;
  free := 0;
  dest[0] := -1;
  readln(n, m);

  for i := 1 to n do
  begin
    next[i] := 0;
    ans[i] := MAXINT - 20;
    read(data);
    a[i] := data;
    if (data <> 0) then
    begin
      inc(last);
      if (last > MAXIN) then
        last := 0;
      q[last].data := i;
      q[last].st := i;
      q[last].ans := 0;
      q[last].prev := 0;
    end;
  end;

  for i := 1 to m do
  begin
    read(x, y);
    add(x, y);
    add(y, x);
  end;

  //______________________________________________________________________________
  p := 0;

  while (size(p, last)) do
  begin
    h := head[q[p].data];
    while (h <> 0) do
    begin
      if (dest[h] <> q[p].prev) then
        if (a[dest[h]] = 0) then    // ?????? ???????????
        begin
          inc(last);
          if (last > MAXIN) then
            last := 0;
          q[last].data := dest[h];
          q[last].st := q[p].st;
          q[last].ans := q[p].ans + 1;
          q[last].prev := q[p].data;
        end
        else
          if (a[dest[h]] <> a[q[p].st]) then  // ????? ???? ???? ????? ???????????? ????
            ans[dest[h]] := min(ans[dest[h]], q[p].ans + 1);
        h := next[h];
    end;
    inc(p);
    if (p > MAXIN) then
      p := 0;
  end;
  //_________________________________________________________________________

  min2 := ans[1];
  for i := 2 to n do
    if (min2 > ans[i]) then
      min2 := ans[i];

  writeln(min2);
  readln;
  readln;
end.

4 4
1 0 2 0
1 2
2 3
3 4
4 1
2

5 4
1 0 2 1 0
1 5
4 5
5 2
2 3
3