#![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 ans=0;
    let mut i=0;

    while let Some(ni)=(i..s.len()).find(|&j|s[j]=='0'){
        i=ni;
        let mut cnt=0;
        loop{
            cnt+=1;
            if i+1>=n{
                break;
            }
            if s[i+1]=='0'{
                i+=1;
            } else if i+2<n && s[i+2]=='0'{
                i+=2;
            } else{
                break;
            }
        }
        ans+=cnt/2;
        i+=1;
    }

    println!("{ans}");
}