(*  average run of alternating coin-flips  *)

SeedRandom(RandomInteger(10000));
  (*  set all elements to zero  *)
XX = Table(0, {1000});
For(j = 1, j <= 1000, j++,
 oldCoin = 0;
 newCoin = RandomInteger()+1;
 While(newCoin != oldCoin,
  oldCoin = newCoin;
  newCoin = RandomInteger()+1;
  Part(XX, j)++
 )
);
N(Mean(XX))