fn main() {
    input!{
        n: usize, p: u128, k: usize,
        tb: [(usize, u128); n],
    }

    const INF : u128 = 1_000_000_000_000_000_000 + 1;

    // dp[i番目まで見た][k個取った] = 最大値
    let mut dp = vec![vec![0u128; k+1]; n+1];
    dp[0][0] = p;

    for i in 0..n {
        for j in 0..=k {
            if j == 0 {
                dp[i+1][j] = dp[i][j];
            }
            else{
                if tb[i].0 == 1 {
                    dp[i+1][j] = max(dp[i][j], dp[i][j-1] + tb[i].1);
                }
                else{
                    dp[i+1][j] = max(dp[i][j], dp[i][j-1] * 2);
                }                
            }
            dp[i+1][j] = min(dp[i+1][j], INF);
        }
    }
    if dp[n][k] == INF { println!("-1"); }
    else { println!("{}", dp[n][k]); }
}
// ---------- begin input macro ----------
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
#[allow(unused)]
use std::{
	io::stderr, io::stdin, io::BufRead, io::Write,
	mem::swap,
	cmp::min, cmp::max,
	cmp::Reverse,
	collections::HashSet, collections::BTreeSet,
	collections::HashMap, collections::BTreeMap,
	collections::BinaryHeap,
	collections::VecDeque,
};