#!/bin/bash

depth=0
horizontal=0
while read current; do
  case "$current" in
    "down "*)
      current_tmp=${current/down /}
      depth=$((depth+current_tmp))
      ;;
    "up "*)
      current_tmp=${current/up /}
      depth=$((depth-current_tmp))
      ;;
    "forward "*)
      current_tmp=${current/forward /}
      horizontal=$((horizontal+current_tmp))
  esac
done

echo $((depth*horizontal))