const MAX_N: usize = 200_000;
const MAX_M: usize = 200_000;
const MAX_K: i64 = 1_000_000_000;
const MAX_Y: i64 = 1_000_000_000;

fn read() -> (usize, i64, Vec<(usize, i64)>) {
    let mut s = String::new();
    use std::io::Read;
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut it = s.trim().split_whitespace();
    let mut next = || it.next().unwrap().parse::<i64>().unwrap();
    let n = next() as usize;
    assert!(1 <= n && n <= MAX_N);
    let m = next() as usize;
    assert!(1 <= m && m <= MAX_M);
    let k = next();
    assert!(1 <= k && k <= MAX_K);
    let mut p = vec![(0usize, 0i64); m];
    for p in p.iter_mut() {
        p.0 = next() as usize;
        assert!(1 <= p.0 && p.0 <= n);
        p.0 -= 1;
        p.1 = next();
        assert!(1 <= p.1 && p.1 <= MAX_Y);
    }
    (n, k, p)
}

fn run() {
    let (n, k, p) = read();
    let mut req = vec![vec![]; n];
    for &(x, y) in p.iter() {
        req[x].push(y);
    }
    let inf = std::i64::MAX / 2;
    let mut a = vec![];
    for (_, req) in req.iter_mut().enumerate() {
        req.sort();
        let mut pre = 0;
        for (j, p) in req.iter().enumerate() {
            a.push((-(req.len() as i64) + 2 * j as i64, *p - pre));
            pre = *p;
        }
        a.push((req.len() as i64, inf));
    }
    a.sort();
    let mut rem = k;
    let mut ans = p.iter().map(|p| p.1).sum::<i64>();
    for &(d, w) in a.iter() {
        let v = w.min(rem);
        rem -= v;
        ans += d * v;
    }
    println!("{}", ans);
}

fn main() {
    run();
}