#![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::(); let a = read_vec::(); if n == 1 { println!("0"); return; } let mut from_right = vec![0; n]; from_right[n - 2] = 1; for i in (0..n - 2).rev() { if a[i] != a[i + 1] { from_right[i] = from_right[i + 1] + 1; } else { from_right[i] = 1; } } debug!(from_right); let mut ans = 0i64; for i in 0..n { if a[i] == 1 { ans += from_right[i]; } } println!("{}", ans); } fn read() -> T { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); s.trim().parse().ok().unwrap() } fn read_vec() -> Vec { read::() .split_whitespace() .map(|e| e.parse().ok().unwrap()) .collect() }