#![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,
    }

    const INF:i64=i64::MAX/64;
    let mut dp=[INF;8];
    dp[7]=0;

    for &c in &s{
        let c=(c as u8-'0' as u8) as usize;
        let mut new=[INF;8];
        for bit in 0..8{
            let next=(bit<<1&7)+c;
            let cur=dp[bit];
            
            if next==0b000 || next==0b001{
                assert!(cur==INF);
            }
            // assert!(next!=0b000 && next!=0b001);

            let mut apply=|a:usize,add:i64|{
                new[a]=new[a].min(cur+add);
            };

            match next{
                0b010=>{
                    apply(next^1,1);
                    apply(next^4,1);
                },
                0b100=>{
                    apply(next^1,1);
                    apply(next^2,1);
                },
                _=>{
                    apply(next,0);
                }
            }
        }
        dp=new;
    }

    let ans=dp.iter().min().unwrap();
    println!("{ans}");
}