/* It is just a binary counter, counting down from an initial pattern */
/* The initial pattern is the answer */
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

typedef long long ll;

int main()
{
  ll bits = 0;
  ll mask;
  int N,i;   // ocelots are 1, zebras are 0
  int line = 0;
  int ch;
  ll count;
  if(scanf("%d",&N)!=1)
    {
      perror("error reading N:");
      exit(1);
    }
  ++line;
  for(i=0;i<N;i++)
    {
      ++line;
      while(isspace(ch = getchar()));
      if(ch != 'O' && ch != 'Z')
	{
	  fprintf(stderr,"Line %d: ",line);
	  perror("error reading animal: ");
	  exit(2);
	}
      if(ch == 'O')
	bits |= (1LL << (N-i-1));
    }
  printf("%lld\n",bits);
  return 0;
}