n = int(input())
s = input()
li = []
i = 0
j = 0
cnt = 0
ans = 0
while i<n:
    while j<n and s[i]==s[j]:
        cnt += 1
        j += 1
    i = j
    li.append(cnt)
    cnt = 0

if s[0] == "#" and len(li)!=1:
    if n%2==0:
        a = sum(li[0::2])
        b = sum(li[1::2])
        if a<b:
            ans = a
        else:
            ans = b
    else:
        a = sum(li[0::2]) - li[-1]
        b = sum(li[1::2])
        if a<b:
            ans = a
        else:
            ans = b
elif s[0] == "." and len(li)!=1:
    if n%2==0 and len(li)!=1:
        a = sum(li[0::2]) - li[0]
        b = sum(li[1::2]) - li[0]
        if a<b:
            ans = a
        else:
            ans = b
    else:
        a = sum(li[0::2]) - li[0]
        b = sum(li[1::2])
        if a<b:
            ans = a
        else:
            ans = b
else:
    ans = 0

print(str(ans))
