This code will set $allowed_city to "yes" if request made from Ukraine (or any other allowed country) OR from Krakow (or any other allowed city).
In /etc/nginx/nginx.conf:
geoip2 /path/to/GeoLite2-City.mmdb {
$geoip2_data_city_name city names en;
$geoip2_data_country_iso_code country iso_code;