#[allow(dead_code)]
fn getline() -> String {
    let mut res = String::new();
    std::io::stdin().read_line(&mut res).ok();
    res
}

#[allow(unused_macros)]
macro_rules! readl {
    ($t: ty) => {
        {
            let s = getline();
            s.trim().parse::<$t>().unwrap()
        }
    };
    ($( $t: ty),+ ) => {
        {
            let s = getline();
            let mut iter = s.trim().split(' ');
            ($(iter.next().unwrap().parse::<$t>().unwrap(),)*)
        }
    };
}

#[allow(unused_macros)]
macro_rules! readlvec {
    ($t: ty) => {
        {
            let s = getline();
            let iter = s.trim().split(' ');
            iter.map(|x| x.parse().unwrap()).collect::<Vec<$t>>()
        }
    }
}

#[allow(unused_macros)]
// macro_rules! debug { ($x: expr) => { println!("{}: {:?}", stringify!($x), $x) } }
macro_rules! debug { ($x: expr) => () }

#[allow(dead_code)]
fn show<T>(iter: T) -> String
where
    T: Iterator,
    T::Item: std::fmt::Display
{
    let mut res = iter.fold(String::new(), |sum, e| sum + &format!("{} ", e));
    res.pop();
    res
}

#[allow(unused_imports)]
use std::cmp::{max, min};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::collections::btree_map::Entry::{Occupied, Vacant};

fn main() {
    use std::io::Write;
    let out = std::io::stdout();
    let mut out = std::io::BufWriter::new(out.lock());
    macro_rules! printf { ($($arg:tt)*) => (write!(out, $($arg)*).unwrap()); }
    macro_rules! printfln { () => (writeln!(out).unwrap()); ($($arg:tt)*) => (writeln!(out, $($arg)*).unwrap()); }
    
    let dx = [-1, -1, 0, 1, 1, 0, -1];
    let dy = [-1, 0, 1, 1, 0, -1, -1];
    let (n, k, p) = readl!(usize, usize, i64);
    let mut qu = VecDeque::new();
    let mut dist: Vec<_> = (0..n).map(|i| vec![-1; i+1]).collect();
    for _ in 0..k {
        let (x, y) = readl!(usize, usize);
        qu.push_back((x-1, y-1, 0));
        dist[x-1][y-1] = 0;
    }
    let check = |x, y| 0 <= x && x < n as i32 && 0 <= y && y <= x;
    while let Some((x, y, d)) = qu.pop_front() {
        for k in 0..dx.len() {
            let nx = x as i32 + dx[k];
            let ny = y as i32 + dy[k];
            if check(nx, ny) && dist[nx as usize][ny as usize] == -1 {
                dist[nx as usize][ny as usize] = d+1;
                qu.push_back((nx as usize, ny as usize, d+1));
            }
        }
    }
    
    let mut csumu: Vec<_> = (0..n+1).map(|i| vec![0; n+1]).collect();
    for i in 0..n {
        for j in 0..i+1 {
            // csumu[i+1][j] = dist[i][j] + csumu[i][j];
            csumu[j][i+1] = dist[i][j] + csumu[j][i];
        }
    }
    let csumu = csumu;

    let mut csuml: Vec<_> = (0..n).map(|i| vec![0; i+2]).collect();
    for i in 0..n {
        for j in 0..i+1 {
            csuml[i][j+1] = dist[i][j] + csuml[i][j];
        }
    }
    let csuml = csuml;


    let mut dp: Vec<_> = (0..n).map(|i| vec![0; i+1]).collect();
    let mut vt: Vec<_> = (0..n).map(|i| vec![0; i+1]).collect();
    for (i, e) in dp[n-1].iter_mut().enumerate() {
        if dist[n-1][i] < p {
            *e = n;
            vt[n-1][i] = dist[n-1][i];
        } else {
            *e = n-1;
            vt[n-1][i] = 0;
        }
    }
    for i in (0..n-1).rev() {
        for j in 0..dist[i].len() {
            let mut r = dp[i+1][j+1];
            let mut val = vt[i+1][j+1] + (csumu[j][r] - csumu[j][i]);
            while i < r && val >= p  {
                let len = r-i;
                val -= csuml[r-1][j + len] - csuml[r-1][j];
                r -= 1;
            }
            dp[i][j] = r;
            vt[i][j] = val;
        }
    }
    
    let mut ans = 0;
    for row in &dp {
        for &e in row {
            ans += n-e;
        }
    }
    printfln!("{}", ans);
}