fn main() {
    let n: usize = {
        let mut line: String = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.trim().parse().unwrap()
    };

    let A: Vec<i64> = {
        let mut line: String = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.split_whitespace()
            .map(|x| x.parse().unwrap())
            .collect()
    };

    let mut ans:i64 = 0;
    let mut score:i64=1;

    for i in 1..n{
        if A[i]==A[i-1]+1{
            score+=1;
        }
        else if score>1{
            ans+=score*(score-1)/2;
            score=1;
        }
    }

    if score>1{
        ans+=score*(score-1)/2;
    }

    println!("{}",ans);



}