N = int( input() )
ans = 0
for i in range( 1, 10, 1 ):
  if i * int( 1e9 + 1 ) <= N:
    ans += 1
for i in range( 1, int( 1e5 ), 1 ):
  f = int( str( i ) + str( i )[ : : -1 ] )
  if f * int( 1e9 + 1 ) > N: break
  ans += 1
  for j in range( 0, 10, 1 ):
    f = int( str( i ) + str( j ) + str( i )[ : : -1 ] )
    if f * int( 1e9 + 1 ) > N: break
    ans += 1
print( ans )