#![allow(unused_imports,non_snake_case,dead_code)]
use std::{cmp::Reverse as Rev,collections::*,iter::*};
use proconio::{marker::*,*};


#[fastout]
fn main(){
    input!{
        n:usize,
        s:Chars,
    }

    let mut es=vec![];
    for i in 0..n-1{
        if &s[i..=i+1]==&['0','0']{
            es.push((i,i+1));
        }
    }
    for i in 1..n-1{
        if &s[i-1..=i+1]==&['0','1','0']{
            es.push((i-1,i+1));
        }
    }
    es.sort_unstable();

    // eprintln!("{:?}",es);
    if es.is_empty(){
        println!("0");
        return;
    }

    let mut ans=0;
    let mut cnt=0;
    let mut prev=es[0].0;

    for &(u,v) in &es{
        cnt+=1;
        if u!=prev{
            ans+=(cnt+1)/2;
            cnt=0;
        }
        prev=v;
    }

    ans+=(cnt+1)/2;
    println!("{ans}");
}