<?php
error_reporting(-1);


function calcCreditSum($creditPerc, $commission, $price, $pay) {
	

    for ($i=0; $i < 20; $i++) {
    	
    	$price += $price * $creditPerc / 100 + $commission;
    	
    	if($price <= $pay){
    		
    		break;
    	}
    	$price += $perc - $pay;
	}
	
	$price += $i*$pay;
	return $price;
}

function calcCreditSumPzdc($creditPerc, $commission, $price, $pay) {
	
	$price += $commission;
	
    for ($i=0; $i < 20; $i++) {
    
    	$price += $creditPerc * $price / 100;
    	
    	if ($price <= $pay){
    		
    		break;
    	}
    	
		$price -= $pay;
		
	}
	
	$price += $i*$pay;
	return $price;
}

$pay = 5000;
$price = 39999;

$balance = calcCreditSum(4, 500, $price, $pay);
echo "Hmcrdt: {$balance}\n";

$balance = calcCreditSum(3, 1000, $price, $pay);
echo "yobabank: {$balance}\n";

$balance = calcCreditSumPzdc(2, 7777, $price, $pay);
echo "pzdc: {$balance}\n";