thing.js

var nthUglyNumber = function(n, a, b, c) {
    const inputs = [a, b, c];
    const curr = [a, b, c];
    
    let counter = n;
    
    while (counter !== 1) {
        const sorted = curr.slice().sort((a, b) => a > b ? 1 : -1);
        let min = sorted[0];
        let minIndex = curr.findIndex((a) => a === min);
        let mid = sorted[1];
        
        let step = Math.floor((mid - min) / inputs[minIndex]) - 1;
        step = Math.min(step, counter - 1);   
        step = Math.max(step, 1);
        
        curr[minIndex] += inputs[minIndex] * step;
        
        counter -= step;
        
        for (let i = 0; i < curr.length; ++i) {
            if (curr[i] === min) {
                curr[i] += inputs[i];
            }
        }        
    }
    
    return Math.min(...curr);
    
};