c# - Datetime Format in two server -

i have 2 different servers each running webservice. codes of webservices same, time format ,and time zones same on both of servers.

the webservice receives information datetime sharepoint server , saves them text.

the problem running saves datetime in 2 different formats.

server 1 format: 15-2-2017 server 2 format: 2-15-2017 

what best way both datetime formats match?

enter code here      private void fetchposts()     {         list<posts> fetchedposts;         string queryfilter = string.empty;          list list = spcontext.web.lists.getbytitle("posts");         datetime newts = timenow;                  {             camlquery camlquery = new camlquery();             if (!string.isnullorempty(pageinfo))             {                 listitemcollectionposition pos = new listitemcollectionposition();                 pos.paginginfo = system.web.httputility.urldecode(pageinfo);                 camlquery.listitemcollectionposition = pos;             }             //  if(lastsynctimestamp!=datetime.minvalue) datetime d = datetime.now;             datetime d = datetime.now;             if(lastsynctimestamp!= d.addmonths(-18))              {                 queryfilter = string.concat(                     "<where>",                         "<gt>",                             "<fieldref name='modified'/>",                              "<value type='datetime' includetimevalue='true'>" + lastsynctimestamp.tostring("s") + "</value>",                         "</gt>",                     "</where>"                 );             }              camlquery.viewxml = string.concat(                 "<view>",                 "<query>",                     queryfilter,                     "<orderby>",                         "<fieldref name='modified' ascending='false'/>",                     "</orderby>",                 "</query>",                 "<rowlimit>" + resultspagesize + "</rowlimit>",               "</view>");             listitemcollection listitems = list.getitems(camlquery);             spcontext.load(listitems);             spcontext.executequery();              fetchedposts = posts.processposts(listitems.tolist<listitem>(), spcontext);             if (listitems.listitemcollectionposition != null)             {                 pageinfo = system.web.httputility.urlencode(listitems.listitemcollectionposition.paginginfo);             }             else             {                 pageinfo = string.empty;             }              addtocache(fetchedposts);         }         while(!string.isnullorempty(pageinfo));          lastsynctimestamp = newts;         savepostcache();     }