package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	var s string
	fmt.Fscan(in, &s)

	if s == "0" {
		fmt.Println(0)
		return
	}

	L := len(s)
	ones := 0
	for i := 0; i < L; i++ {
		if s[i] == '1' {
			ones++
		}
	}

	if ones == 1 {
		fmt.Println(L / 2)
	} else {
		fmt.Println((L + 1) / 2)
	}
}