use std::io::Read; fn main() { let mut buf = String::new(); std::io::stdin().read_to_string(&mut buf).unwrap(); let mut iter = buf.split_whitespace(); let n: usize = iter.next().unwrap().parse().unwrap(); let mut a: Vec = Vec::with_capacity(n); for _ in 0..n { let x: i32 = iter.next().unwrap().parse().unwrap(); a.push(x - 1); } let mut b: Vec = vec![-1; n]; for (i, x) in a.iter().enumerate() { let j: usize = *x as usize; if b[j] >= 0 { if b[j] == 0 && i == n - 1 { println!("1"); } else { println!("-1"); } return; } b[j] = i as i32; } println!("0"); }