fn main() {
    let mut input = String::new();
    let _ = std::io::stdin().read_line(&mut input);
    let input: Vec<i32> = input.trim().split_whitespace().map(|n| n.parse().unwrap()).collect();
    let mut prev = 0;
    let mut result = 10;
    for i in input {
        if i - prev > 1 {
            result = i - 1;
            break;
        }
        prev = i;
    }
    println!("{}", result);
}