package main

import . "fmt"

func main() {
	var n int
	var s string
	Scan(&n, &s)
	b := []byte(s)
	r := 0
	one, zero := 0, 0
	ans := 0
	for i, c := range b {
		if c == '1' {
			one++
		} else {
			zero++
			if i > 0 && zero > one {
				b[i] = '1'
				zero--
				one++
				ans++
			}
		}
		for one > zero && one > 1 && r <= i {
			if b[r] == '1' {
				one--
			} else {
				zero--
			}
			r++
		}
	}
	Println(ans)
}