import numpy as np

N = int(input())
S = input()
L = [0] * N
for i in range(N):
    if S[i] == "#":
        # white
        L[i] = 1
    else:
        L[i] = 0
L = np.array(L, dtype=np.int8)
L2 = np.zeros(N, dtype=np.int8)
ans = np.abs((L - L2)).sum()
for i in range(N):
    L2[N-1-i] = 1
    ans_tmp = np.abs((L - L2)).sum()
    ans = min(ans, ans_tmp)
print(ans)