use proconio::input;

fn main() {
    input! {
        n: usize, m: usize,
        mut cards: [(usize, usize); n]
    }
    cards.sort_unstable_by_key(|t| t.0);

    let mut dp = vec![-1isize; m + 1];
    dp[0] = 0;

    for &(c, d) in &cards {
        let max = m.saturating_sub(c) / 2;
        for i in (0..=max).rev() {
            if dp[i] == -1 {
                continue;
            }

            let j = i * 2 + c;
            dp[j] = dp[j].max(dp[i] + d as isize);
        }
    }

    let ans = dp.iter().max().unwrap();
    println!("{}", ans);
}