The problem is from codeforces: http://codeforces.com/problemset/problem/180/C
Let n be the number of lower-cases that have encountered so far from left to right; So everytime there is an uppercase letter, you check if n > 0, then increase the answer and decrease n.
So letter by letter, we virtually change any past lowercase letters to uppercases.
#!/usr/bin/env python
from sys import stdin
s = stdin.readline()
ans = 0
a = 0
for i in s:
if i.islower():
a += 1
elif i.isupper() and a > 0:
a -= 1
ans += 1
print ans
–EOF (The Ultimate Computing & Technology Blog) —
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