#!/bin/bash

regex="mul\(([0-9]{1,3}),([0-9]{0,3}))"

acc=0
while read line; do
    if [[ $line =~ $regex ]] then
        n1=${BASH_REMATCH[1]}
        n2=${BASH_REMATCH[2]}
        acc=$(expr $n1 \* $n2 + $acc)
    fi
done <<< $(grep -Eo $regex input.txt)
echo $acc