fn main() {
    let n : usize = input();
    let a : Vec<i64> = input_vec();

    if a[0] == 0 && a[1] - (a[2] - a[1]) <= 0 { println!("No"); return; }
    let mut a : Vec<_> = a.windows(2).filter(|a| a[0]!=0 && a[1]!=0).map(|a| a[1] - a[0]).collect();
    a.dedup();
    if a.len() <= 1 {
        println!("Yes");
    } else {
        println!("No");
    }
}

#[allow(dead_code)] fn input<T: std::str::FromStr>() -> T { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); s.trim().parse().ok().unwrap() } #[allow(dead_code)] fn input_t<T: std::str::FromStr, U: std::str::FromStr>() -> (T, U) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap()) } #[allow(dead_code)] fn input_t3<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr>() -> (T1, T2, T3) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap(), s[2].parse().ok().unwrap()) } #[allow(dead_code)] fn input_t4<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr, T4: std::str::FromStr>() -> (T1, T2, T3, T4) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap(), s[2].parse().ok().unwrap(), s[3].parse().ok().unwrap()) } #[allow(dead_code)] fn input_t5<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr, T4: std::str::FromStr, T5: std::str::FromStr>() -> (T1, T2, T3, T4, T5) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap(), s[2].parse().ok().unwrap(), s[3].parse().ok().unwrap(), s[4].parse().ok().unwrap()) } #[allow(dead_code)] fn input_vec<T: std::str::FromStr>() -> Vec<T> { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); s.trim().split_whitespace().map(|s| s.parse().ok().unwrap()).collect() }