use std::io;

fn main() {
    let mut s = String::new();
    io::stdin().read_line(&mut s).ok();
    let _n = s.trim().parse::<i32>().ok();
    s = String::new();
    io::stdin().read_line(&mut s).ok();
    let mut v: Vec<f32> = s.split_whitespace().map(|cs| cs.parse().ok().unwrap()).collect();
    
    loop {
        if v.len() < 2 { break; }
        let n1 = v.pop().unwrap();
        let n2 = v.pop().unwrap();
        let r: f32 = (n1 + n2) / 2.0;
        v.push(r);
    }

    println!("{}", v.pop().unwrap());
}