n = input()
s = list(input())

ans = 0

for i in range(len(s)-1):
	if(s[i] == "#" and s[i+1] == "."):
		if(i == 0):
			s[i] = "."
		else if(i > 0 and s[i-1] != "#"):
			s[i] = "."
		else:
			s[i+1] = "#"
		ans += 1

print(ans)
