#!/bin/bash

rules=()
n_step=10
read polymer
read

while read line; do
  rules+=( ${line% ->*}'|'${line#*-> } )
done

for ((i=0; i<$n_step; i++)); do
  polymer_size=0
  while [ $polymer_size -lt ${#polymer} ]; do
    polymer_size=${#polymer}
    for rule in ${rules[@]}; do
      polymer=${polymer//${rule:0:2}/${rule:0:1}'|'${rule:3:1}'|'${rule:1:1}}
    done
  done
  polymer=${polymer//'|'/}
done

occurences=( $(printf "%s\n" $(sed 's/\(.\)/\1 /g' <<< $polymer) | sort | uniq -c \
                   | sort -nr | sed 's/.$//') )
echo $((occurences[0]-occurences[-1]))