#include <stdio.h>
#include <stdlib.h>
int main(void) {
int ctr = 0;
scanf("%d\n", &ctr);
char str[ctr], curr;
for(int i = 0; i < ctr; i++){
scanf("%c\n", &curr);
str[i] = curr == 'Z' ? '0' : '1';
}
str[ctr] = '\0';
printf("%ld", strtol(str, NULL, 2));
}