import bisect
import sys
from math import isqrt
from typing import List, Tuple

sys.setrecursionlimit(10 ** 6)

MOD = 998244353

int1 = lambda x: int(x) - 1
input = lambda: sys.stdin.readline().rstrip('\n')
ii = lambda: int(input())
vi = lambda: list(map(int, input().split()))
vi1 = lambda: list(map(int1, input().split()))


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()),
          sep='; ', file=sys.stderr, flush=True)


def main():
    n = ii()
    s = input()
    a = [float('inf')] * n
    b = [float('inf')] * n
    for i in range(n):
        if s[i] == '#':
            a[i] = 0
        elif i > 0:
            a[i] = a[i - 1] + 1

    for i in range(n - 1, -1, -1):
        if s[i] == '#':
            b[i] = 0
        elif i != n - 1:
            b[i] = b[i + 1] + 1

    print(1 - max((min(a[i], b[i]), -i) for i in range(n))[1])


def _start():
    if (ret := main()) is not None:
        print(*ret) if isinstance(ret, List) or isinstance(ret, Tuple) else print(ret)


if __name__ == '__main__':
    _start()