Cannot install piwik [500 error]



I have VPS with Ubuntu and apache.

When i go to piwik installation directory, i find this error in error log:

[09-Nov-2015 15:38:11 UTC] PHP Fatal error:  Uncaught exception 'Exception' with message 'The configuration file {/var/www/html/public_html/mystatistics/config/config.ini.php} has not been found or could not be read.' in /var/www/html/public_html/mystatistics/core/Application/Kernel/EnvironmentValidator.php:64
Stack trace:
#0 /var/www/html/public_html/mystatistics/core/Application/Kernel/EnvironmentValidator.php(45): Piwik\Application\Kernel\EnvironmentValidator->checkConfigFileExists('/var/www/html/b...', false)
#1 /var/www/html/public_html/mystatistics/core/Application/Environment.php(185): Piwik\Application\Kernel\EnvironmentValidator->validate()
#2 /var/www/html/public_html/mystatistics/core/Application/Environment.php(94): Piwik\Application\Environment->validateEnvironment()
#3 /var/www/html/public_html/mystatistics/piwik.php(56): Piwik\Application\Environment->init()
#4 {main}
  thrown in /var/www/html/public_html/mystatistics/core/Application/Kernel/EnvironmentValidator.php on line 64

Access log gives 500 error:

81.7.x.x - - [09/Nov/2015:10:38:11 -0500] "GET /mystatistics/piwik.php?url= HTTP/1.1" 500 169 "" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:42.0)

If i go to next installation step, i get this error in browser:

GET request to piwik.php failed. Try whitelisting this URL from 
HTTP Authentication and disable mod_security (you may have to ask your 
webhost). For more information about the error, check your web server 
error log file.
After making this change, restart your web server.

If i create config.ini.php before instaliation, then piwik tries to load whole page, but not prosceed installation…

Please advise. I do not have mod_security enabled.