MOD=10**9+7
cnt=0; sum=0; prev=nil; can=true; h=Hash.new(0)
def gs() gets.chomp end
def gi() gets.to_i end
def gsmi() gets.chomp.split.map(&:to_i) end

def desc(ar) ar.sort!{|x,y|y<=>x} end
def min(a,b) a<=b ? a : b end
def max(a,b) a>=b ? a : b end
def sum(ar) ar.inject(:+) end

def C(a,b) b==0||a==b ? 1 : (b=a-b if a/2<b;(a-b+1..a).inject(:*)/(1..b).inject(:*)) end

def puts_yesno(can) puts(can ? 'Yes' : 'No') end
def putsend(s) puts s; exit end
def debug(k,v) puts "#{k}:#{v}" end
########### ( ˘ω˘ )ｽﾔｧ… ###########
s0=gs
l=s0.length
putsend 0 if l==1

c=l/2
s=""
t=""
if l%2==0
  s=s0[0..c-1]
  t=s0[c..-1].reverse
else
  s=s0[0..c-1]
  t=s0[c+1..-1].reverse
end
l.times do |i|
  cnt+=1 if s[i]!=t[i]
end

puts cnt