import sys

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

score1 = 0
score2 = 0
length = 1
check = S[0]
A = []
B = []
flag = 0

for i in range(N-1):
    if S[i] == S[i+1]:
        length += 1
    else:
        A.append(length)
        length = 1

if length != 1:
    A.append(length)

if len(A) != 0:
    if S[-1] != S[-2]:
        A.append(1)

if len(A) <= 1:
    print(0)
    sys.exit()

if S[0] == ".":
    A.pop(0)

if S[len(S)-1] == "#":
    A.pop(-1)

if len(A) == 0:
    print(0)
    sys.exit()

for i in range(len(A)):
    if i % 2 == 0:
        score1 += A[i]
    else:
        score2 += A[i]
        
ans = min(score1,score2)

if S[0] == "#":
    score3 = A[0] + score2 - A[1]

    ans = min(ans,score3)

if S[-1] == ".":
    score4 = A[len(A)-1] + score1 - A[len(A)-2]

    ans = min(ans,score4)


print(ans)