#!/bin/python3
s = input()

c0 = 0
c1 = 0

n = len(s)
for a in range (int((n -2) / 2), -1, -1):
    b = n  - 1 - a
    if s[a] == s[b]:
        m = 0
    else:
        m = 1

    nc0 = 1000000000
    nc1 = 1000000000

    for i in range(0, 3):
        if ( (m==0) | (i != 0) ) & ( (m != 0) | (i != 1)):
            if (i >= 1):
                nc0 = min(nc0, i + c1)
            if (i != 1):
                nc0 = min(nc0, i + c0)
        if ( (m!=0) | (i != 0)):
            if (i >= 1):
                nc1 = min(nc1, i + c1)
            if (i != 1):
                nc1 = min(nc1, i + c0)

    c0 = nc0
    c1 = nc1
    b += 1

print(c0)