import std.stdio, std.conv, std.array, std.string, std.algorithm, std.container, std.range, core.stdc.stdlib, std.math, std.typecons;
T[][] combinations(T)(T[] s, in int m) {   if (!m) return [[]];   if (s.empty) return [];   return s[1 .. $].combinations(m - 1).map!(x => s[0] ~ x).array ~ s[1 .. $].combinations(m); }

void main() {
  auto S = readln.chomp;
  auto L = S.length;

  int distinct_count;
  foreach(i; 0..L/2) {
    if (S[i] != S[L-i-1]) distinct_count++;
  }
  writeln(distinct_count);
}
