# -*- coding: utf-8 -*-
import sys
# ----------------------------------------------------------------
# Use Solve Function

def solve(lines):
    N = int(lines.pop(0))
    S = lines.pop(0)
    # reverse
    S = S[::-1]
    # 白が現れるまで省く
    idx = S.index('.')
    S = S[idx:]
    # あとは少ない方を裏返せば良い
    print(min(S.count('.'), S.count('#')))


lines = [x.strip() for x in sys.stdin.readlines()]
solve(lines)