#![allow(
    dead_code,
    non_snake_case,
    unused_imports,
    unused_mut,
    unused_variables,
    while_true,
    unused_assignments,
    clippy::needless_range_loop,
    clippy::ptr_arg,
    clippy::type_complexity,
    clippy::unnecessary_cast
)]
use proconio::{
    input,
    marker::{Chars, Usize1 as usize1},
};
use std::collections::{BinaryHeap, HashMap, HashSet, VecDeque};

fn main() {
    input! {
        N: usize,
        mut S: Chars,
    };

    let mut ans = 0;
    for i in 0..N {
        let mut c0 = 0;
        for k in i.saturating_sub(2)..i {
            if S[k] == '0' {
                c0 += 1;
            }
        }
        if c0 > 0 && S[i] == '0' {
            ans += 1;
            S[i] = '1';
        }
    }

    println!("{}", ans);
}