JSFiddle - React, Tailwind, and code Playground

JavaScript

var fingers = 0;
var hands = 0;
var FINGER_NUMBER = 5;

/* MEAT */
function sum(a,b){
    while(a-- > 0) {
        finger_inc();
    }
    while(b-- > 0) {
        finger_inc();
    }
    
    return count_hands_and_fingers(); // We count the number of hands and fingers
}

/* Private functions */
function finger_inc(){
    if(++fingers >= FINGER_NUMBER) {
        hands++;
        fingers = 0;
    }
}

function count_hands_and_fingers() {
    var total_count = 0;
    total_count = hands * FINGER_NUMBER;
    total_count += fingers;
    return total_count;
}

document.write(sum(1,50));