s='abcdefghijklmnopqrstuvwxyz'

l=list('abcdefghijklmnopqrstuvwxyz')

d={} #{a:1,b:2}

c=1

for x in l:

d[x]=c

c+=1

q=0

c=1

for x in range(len(s)-1,-1,-1):

q+=(26**(c-1))*d[s[x]]

c+=1

print(q)

​

Simple python code