N = int(input())
S = input()
# . = しろ
# # = 黒
# #の横に.がないようにしたい
# #の横に.があったら#を.に変える
# or #の横に.があったら.を#に変える

# テストケース
"""
11
#..#.##.##.
"""
# => .....# = 2

def inorderReplace(S , N): 
    S = list(S)
    cnt = 0
    for i in range(N - 1) : 
        nowChar = S[i]
        nextChar = S[i + 1]
        if nowChar == "#" and nextChar == "." : 
            cnt += 1
            S[i + 1] = "#"
    return cnt

def preorderReplace(S , N) : 
    S = list(S)
    cnt = 0
    for i in reversed(range(1, N)) : 
        nowChar = S[i]
        prevChar = S[i - 1]
        if prevChar == "#" and nowChar == "." : 
            cnt += 1
            S[i - 1] = "."
    return cnt


cnt = inorderReplace(S , N)
cnt2 = preorderReplace(S , N)
print(min(cnt , cnt2))