#![allow(unused_imports)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;
use std::ops::Bound::*;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let n = read::<usize>();
    let a = read_vec::<i64>();
    let a = a.into_iter().collect::<HashSet<_>>();

    let mut cands = vec![];
    for &anum in &a {
        cands.push(anum);
        cands.push(anum + 1);
    }
    cands.sort();
    cands.dedup();

    let mut dp = HashMap::new();
    for cand in cands {
        if a.contains(&cand) {
            *dp.entry(cand).or_insert(0) += 1i64;
        }
        if a.contains(&(cand - 1)) {
            dp.entry(cand - 2).or_insert(0);
            *dp.entry(cand).or_insert(0) += dp[&(cand - 2)];
        }
    }
    let ans = dp.values().sum::<i64>();
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}