<?php

error_reporting(-1);

function countPayments ($percent, $servicePayment, $creditBalance, $monthlyPayment, $costOfDiscovery){

    $paymentTotal = 0;
    $creditBalance +=$costOfDiscovery;

    for ($month = 1; $creditBalance >= 0; $month++){

	    $creditBalance = $creditBalance * $percent + $servicePayment;

        if ($creditBalance <= 5000){
	        $paymentTotal += $creditBalance;
	        break;
        } 

	    $paymentTotal += $monthlyPayment;		    
	    $creditBalance -= $monthlyPayment;
    }
    return $paymentTotal;
}

$creditBalance = 39999;
$monthlyPayment = 5000;

$homoCreditTotal = countPayments (1.04, 500, $creditBalance, $monthlyPayment, 0);
$softbankTotal = countPayments (1.03, 1000, $creditBalance, $monthlyPayment, 0);
$strawberryBankTotal = countPayments (1.02, 0, $creditBalance, $monthlyPayment, 7777);

echo "homoCredit: $homoCreditTotal руб.\n";
echo "softbank: $softbankTotal руб.\n";
echo "strawberryBank: $strawberryBankTotal руб.\n";