use proconio::input;

fn main() {
    input! {
        n: usize,
        cards: [(usize, usize); n],
    }

    let mut ans = 0;
    for &(a, b) in &cards {
        let i = a.trailing_zeros().min(3) as usize;
        ans += i * b;
    }
    ans /= 3;
    println!("{ans}");
}