package main

import . "fmt"
import . "slices"

func main() {
	var n int
	var s string
	Scan(&n, &s)
	ans := solve(n, s)
	Println(ans)
}

func solve(n int, s string) int {
	bs := []byte(s)
	Reverse(bs)
	ans := 0
	c := 1
	for i, b := range bs {
		if c > 0 {
			c--
		}
		if b == '#' {
			ans = max(ans, i+1+c)
			c += 2
		}
	}
	return ans
}

func init() {
	check()
}

func check() {
	n := 10
	b := make([]byte, n)
	for i := 0; i < (1<<n); i++ {
		for j := 0; j < n; j++ {
			if ((i>>j)&1) == 0 {
				b[j] = '.'
			} else {
				b[j] = '#'
			}
		}
		s := string(b)
		a1 := solve(n, s)
		a2 := brutefoce(n, s)
		if a1 != a2 {
			panic(Sprintf("n=%d,s=%s,a1=%d,a2=%d",n,s,a1,a2))
		}
	}
}

func brutefoce(n int, s string) int {
	bs := append([]byte(s), '.')
	ans := 0
	for {
		bs[n] = '.'
		found := false
		for i := 0; i < n; i++ {
			if bs[i] == '.' {
				continue
			}
			found = true
			if bs[i+1] == '.' {
				bs[i] = '.'
				bs[i+1] = '#'
				i++
			}
		}
		if !found {
			break
		}
		ans++
	}
	return ans
}