import qualified Data.Vector as V
import Data.Array

odd_solver::V.Vector Char->Int
odd_solver v = let m = div (V.length v) 2 in
               let s = div (V.length (last (filter same [V.slice (m-s) ((2*s)+1) v |s <- [0..m]]))) 2in
               m+s+1

even_solver::V.Vector Char->Int
even_solver v = let m = div (V.length v) 2 in
                let s = div (V.length (last (filter same [V.slice (m-s) (2*s) v | s <- [0..m]]))) 2 in
                m+s

same::V.Vector Char->Bool
same v        =if v == V.empty then True else V.foldl (\ b -> \ x -> ((V.head v)==x)&&b) True v

total_solver::String->Int
total_solver ls = let v = V.fromList ls in
                  if mod (V.length v) 2 == 1 then odd_solver v else even_solver v




impl_odd::Array Int Char->Int->Int
impl_odd ar size = let m = div size 2 in
                  m+1+(foldl_with_cond (\s -> \(i,j) -> s+1) (-1)  (\(i,j)->(ar!i==ar!(m+1))&&(ar!j==ar!(m+1))) [(m+1-j,m+1+j)|j<-[0..m]])


impl_even::Array Int Char->Int->Int
impl_even ar size = let m = div size 2 in
                   m+(foldl_with_cond (\s -> \(i,j)->s+1) 0 (\(i,j)->(ar!i==ar!(m+1))&&(ar!j==ar!(m+1))) [(m+j,m-j+1)|j<-[1..m]])



foldl_with_cond::(a->b->a)->a->(b->Bool)->[b]->a
foldl_with_cond _ now _    []    = now
foldl_with_cond f now cond (x:xs)= if cond x then foldl_with_cond f (f now x) cond xs
                                            else now

impl_total::String->Int
impl_total ls = let n = length ls in
                let ar = listArray (1,n) ls in
                if mod n 2 == 1 then impl_odd ar n else impl_even ar n

main::IO()
main=do
  str<-getLine
  print (impl_total str)
