SET BIT IN STRING

Chef has been provided a $string$ $of$ $lowercase$ $alphabets$, and his task is to find the total number of set bits in the string when string is in converted further into $integer$. Chef knows that all alphabets can be numbered from $1-26$, but while converting into decimal one also has to make sure of the position in decimal. For Ex-$abc$ $is$ $123$ $because$, $a$ $is$ $at$ $100th$ $place$ $b