N = int(input())
S = input()
def count(_S):
    _S = input().rstrip('#').lstrip('.')
    if len(_S) == 0 :
        return 0
    numSW = _S.count('.')
    numSB = _S.count('#')
    SR = _S.lstrip('#').rstrip('.')
    numSR = len(_S) - len(SR)
    if numSW <= numSB and numSW <= numSR:
        return numSW
    elif numSB <= numSW and numSB <= numSR:
        return numSB
    else:
        return numSR + count(SR)
print(count(S))