package main

import (
	"fmt"
	"strings"
)

func main() {
	var s string
	fmt.Scan(&s)
	if s == "0" {
		fmt.Println(0)
	} else if strings.Count(s, "1") > 1 {
		fmt.Println((len(s) + 1) / 2)
	} else {
		fmt.Println(len(s) / 2)
	}
}