#!/bin/bash

depth=0
horizontal=0
while read current; do
  if [[ "$current" == "down "* ]]; then
    current_tmp=${current/down /}
    depth=$((depth+current_tmp))
  elif [[ "$current" == "up "* ]]; then
    current_tmp=${current/up /}
    depth=$((depth-current_tmp))
  elif [[ "$current" == "forward "* ]]; then
    current_tmp=${current/forward /}
    horizontal=$((horizontal+current_tmp))
  fi
done

echo $((depth*horizontal))