fn main() {
    input! {
        h: usize,
        w: usize,
        n: usize,
        p: [(usize1, usize1); n],
    }
    let mut p = p;
    p.sort();
    p.reverse();
    let mut ans = 0u64;
    let mut height = vec![0; w];
    let mut stack: Vec<(u32, u32)> = vec![];
    for i in 0..h {
        height.iter_mut().for_each(|h| *h += 1);
        while p.last().map_or(false, |p| p.0 == i) {
            height[p.pop().unwrap().1] = 0;
        }
        stack.clear();
        let mut sum = 0;
        for &h in height.iter() {
            let mut w = 1;
            while stack.last().map_or(false, |p| p.0 >= h) {
                let p = stack.pop().unwrap();
                sum -= p.0 * p.1;
                w += p.1;
            }
            sum += h * w;
            ans += sum as u64;
            stack.push((h, w));
        }
    }
    println!("{}", ans);
}

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