<?php
error_reporting(-1);
function kappa($creditSum, $payout, $percent, $payment, $payment1){
	$creditSum = $creditSum + $payment1;
	$paymentTotal = 0;
	for($i = 0; $i <666; $i++){
		$creditSum = $creditSum * $percent + $payment - $payout;
		$paymentTotal = $paymentTotal + $payout;
			if($creditSum < 0){
				$paymentTotal = $paymentTotal + $creditSum;
				break;
			}
		}
	return $paymentTotal;
}	
$creditSum = 39999;
$payout = 5000;
$homoCreditTotal = kappa($creditSum, $payout, 1.04, 500, 0);
$softbankTotal = kappa($creditSum, $payout, 1.03, 1000, 0);
$strawberryBankTotal = kappa($creditSum, $payout, 1.02, 0, 7777);
echo "Homocredit: {$homoCreditTotal} руб.\n";
echo "Softbank: {$softbankTotal} руб.\n";
echo "StrawberryBank: {$strawberryBankTotal} руб.\n";