#!/usr/bin/env bash

# check if a command-line argument was provided
if [ -z "$1" ]
then
  echo "Error: invalid input"
  exit 1
fi

square=$1

# check if the square number is valid
if [[ "$square" != "total" ]] && (( square < 1 || square > 64 ))
then
  echo "Error: invalid input"
  exit 1
fi

if [[ $square == "total" ]]
then
    total_grains=0
        for ((square=1; square<=64; square++))
    do
        grains_on_square=$(echo "2^($square-1)" | bc)
        
        # use arbitrary precision arithmetic using basic calculator (bc)
        total_grains=$(echo "$total_grains + $grains_on_square" | bc)
    done
    echo $total_grains
else
    grains_on_square=$(echo "2^($square-1)" | bc)
    echo $grains_on_square
fi