Ubuntu 15.10 error while install mysql-server

i've been trying to install mysql-server but while installing i encounter this error what might be the solution to it ?`

 sudo aptitude install mysql-server
The following NEW packages will be installed:
  mysql-server-5.6{a} 

The following partially installed packages will be configured:
  mysql-server 
0 packages upgraded, 1 newly installed, 0 to remove and 5 not upgraded.
Need to get 0 B/5,744 kB of archives. After unpacking 52.4 MB will be used.
Do you want to continue? [Y/n/?] y
Preconfiguring packages ...              
(Reading database ... 387903 files and directories currently installed.)
Preparing to unpack .../mysql-server-5.6_5.6.27-0ubuntu1_amd64.deb ...
Aborting downgrade from (at least) 10.0 to 5.6.
If are sure you want to downgrade to 5.6, remove the file

/var/lib/mysql/debian-*.flag and try installing again.
dpkg: error processing archive /var/cache/apt/archives/mysql-server-5.6_5.6.27-0ubuntu1_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
Errors were encountered while processing:
 /var/cache/apt/archives/mysql-server-5.6_5.6.27-0ubuntu1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
Failed to perform requested operation on package.  Trying to recover:
dpkg: dependency problems prevent configuration of mysql-server:
 mysql-server depends on mysql-server-5.6; however:
  Package mysql-server-5.6 is not installed.


dpkg: error processing package mysql-server (--configure):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 mysql-server