import strutils

var S = readLine(stdin)
var Slen = S.len()

if Slen mod 2 == 0 :
  var
    Scopy1 = S
    Scopy2 = S
  delete(Scopy1, int(Slen/2), Slen-1)
  delete(Scopy2, 0, int(Slen/2)-1)
  if Scopy1 == Scopy2 :
    echo "YES"
  else:
    echo "NO"
else:
  echo "NO"