const INF: usize = 1usize << 60;

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<_> = a.trim().split_whitespace().collect::<Vec<_>>().join("").split('2').map(|s| s.chars().collect::<Vec<_>>()).collect();

    let zeros = a.iter().filter(|&v| v.len() > 0).map(|v| v.iter().filter(|&&c| c == '1').count()).sum::<usize>();
    let one_cnt = a.iter().filter(|&v| v.len() > 0).map(|v| v.iter().filter(|&&c| c == '1').count()).collect::<Vec<_>>();
    let size_cnt = a.iter().filter(|&v| v.len() > 0).map(|v| v.len()).collect::<Vec<_>>();
    let mut dp = vec![vec![INF; n+1]; size_cnt.len()+1];
    dp[0][0] = 0;
    for i in 0..size_cnt.len() {
        let to_zero_cnt = size_cnt[i] - one_cnt[i];
        for j in 0..=n {
            if dp[i][j] == INF { continue; }
            dp[i+1][j+size_cnt[i]] = dp[i+1][j+size_cnt[i]].min(dp[i][j] + to_zero_cnt);
            dp[i+1][j] = dp[i+1][j].min(dp[i][j]);
        }
    }
    if dp[size_cnt.len()][zeros] == INF {
        println!("-1");
    } else {
        println!("{}", dp[size_cnt.len()][zeros]);
    }
}