!7

p {
  assertEquals("0", calc("0"));
  assertEquals("1", calc("1"));
  assertEquals("1", calc("1!"));
  assertEquals("1", calc("0!"));
  assertEquals("1", calc("!0"));
  assertEquals("0", calc("!1"));
  assertEquals("0", calc("!0!"));
  assertEquals("1", calc("!!0!"));
  assertEquals("0", calc("!!0"));
}

sS calc(S s) {
  ret applyUntilStable(s, func(S s) { s.replaceAll(".!", "1").replace("!0", "1").replace("!1", "0") });
}