program hanoi;
var
step:longint;
i,n:integer;
goal:array[1..31] of byte;
procedure p(k:integer;a,b,c:integer);
begin
if k=0 then exit;
if goal[k]=b then
 begin
  step:=step+trunc(exp((k-1)*ln(2)));
  p(k-1,c,b,a);
 end
else if goal[k]=c then begin writeln(-1); halt; end
else p(k-1,a,c,b);
end;
begin
readln(n);
for i:=1 to n do read(goal[i]);
step:=0;
p(n,1,2,3);
writeln(step);
end.

here's mine
#include <stdio.h>

int n, s[50], s1[] = {0, 1, 2, 2, 3, 3, 1, 1, 2, 2, 3, 3, 1},
              s2[] = {0, 1, 3, 3, 2, 2, 1, 1, 3, 3, 2, 2, 1};


int is(int lev, long pos)
{
    if (pos % 12 == 0) pos++;
    return (lev & 1) ? s1[pos % 12] : s2[pos % 12];
}

long baga_mare(int lev, long pos)
{
    long fiu;
    if (lev == n) return pos;
    fiu = 2 * pos - 1;
    if (s[n - lev] == is(lev + 1, fiu))
        return baga_mare(lev + 1, fiu);
    fiu = 2 * pos;
    if (s[n - lev] == is(lev + 1, fiu))
        return baga_mare(lev + 1, fiu);
    return 0;
}

int main()
{
    int i;

    scanf("%d", &n);
    for (i = 1; i <= n; scanf("%d", s + i++));

    printf("%ld\n", baga_mare(0, 1) - 1);

    return 0;
}