// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
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_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_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 ----------

fn run() {
    input! {
        n: usize,
        m: usize,
        k: i64,
        p: [(usize1, i64); m],
    }
    let mut req = vec![vec![]; n];
    for &(x, y) in p.iter() {
        req[x].push(y);
    }
    let mut h = std::collections::BinaryHeap::new();
    for (i, req) in req.iter_mut().enumerate() {
        req.sort();
        if req.is_empty() {
            h.push((0, i, 0));
        } else {
            h.push((req.len() as i64, i, 0));
        }
    }
    let mut cnt = vec![0i64; n];
    let mut rem = k;
    let mut ans = p.iter().map(|p| p.1).sum::<i64>();
    while rem > 0 {
        let (diff, x, y) = h.pop().unwrap();
        if req[x].len() <= y {
            ans -= diff * rem;
            cnt[x] += rem;
            rem = 0;
        } else {
            let p = rem.min(req[x][y] - cnt[x]);
            ans -= diff * p;
            cnt[x] += p;
            rem -= p;
            h.push((diff - 2, x, y + 1));
        }
    }
    println!("{}", ans);
}

fn main() {
    run();
}