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 mut a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    while !a.is_empty() && a[a.len()-1] == 0 {
        a.pop();
    }
    if a.is_empty() {
        println!("Yes");
        return;
    }
    let n = a.len();
    if a[n-1] == n && (a[0] == 0 || a[0] == 1) && (1..n-1).filter(|&i| a[i] != i).count() == 0 {
        println!("Yes");
    } else {
        println!("No");
    }
}