N = int(input())

S = str(input())

# cnt = 0
# target = S[0]
# for i in range(1, N):
#     if target == '#' and S[i] == '.':
#         cnt += 1
#         target = '#'  # 黒に変える
#         continue
#
#     if S[i] == '#':
#         target = '#'
#     else:
#         target = '.'
#
# cnt_2 = 0
# aim = S[-1]
# for i in range(N-1, -1, -1):
#     if aim == '.' and S[i] == '#':
#         cnt_2 += 1
#         aim = '.'
#         continue
#
#     if S[i] == '#':
#         aim = '#'
#     else:
#         aim = '.'
#
#
# print(int(min(cnt, cnt_2)))

black = 0
white = 0
for i in range(N):
    if S[i] == '#':
        black += 1
    else:
        white += 1

less_color = min(black, white)
if (black < white) and S[-1] == '#':
    less_color -= 1

print(less_color)
