```python

N = int(input())
S = input()

S = list(S)
white_count = S.count(".")
black_count = S.count("#")
count = 0

if white_count < black_count:

    for i in range(len(S)-1):
        if (S[i]=="#")and(S[i+1]=="."):
            count += 1
            S[i+1] == "#"
else :
	S = reversed(S)
    for i in reversed(range(len(S)-1)):
      
        if (S[i]=="#")and(S[i-1]=="."):
            count += 1
            S[i] == "."

print(count)
```