# 18238 ZOAC 2

# 18238
tmp = input()
alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

cnt = 0 
now = alpha.index('A')

for i in tmp:
  start = alpha.index(i)
  if abs(start-now) > 12 :
    cnt = cnt+ 26 - abs(start-now)
  else:
    cnt = cnt + abs ( start-now )
  now = start

print (cnt)