#include <bits/stdc++.h>
using namespace std;
#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define YES() printf("YES\n")
#define NO() printf("NO\n")
#define Yes() printf("Yes\n")
#define No() printf("No\n")
#define in(x,y,h,w) x >= 0 && x < h && y >= 0 && y < w

#define int long long
//typedef    long long          ll;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      P;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
 
const int INF=1e+18;
const double EPS=1e-9;
const int MOD=1000000007;
 
const int dx[]={-1,-1,0,0,1,1},dy[]={-1,0,-1,1,0,1};

int num[4010][4010],d[4010][4010],a[4010][4010],b[4010][4010];

signed main(){
	int n,k,p,ans = 0;
	cin >> n >> k >> p;
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= i;j++) d[i][j] = INF;
	}
	queue<P> que;
	for(int i = 0;i < k;i++){
		int x,y;
		cin >> x >> y;
		d[x][y] = 0;
		que.push(mp(x,y));
	}
	for(int t = 0;;t++){
		int siz = que.size();
		if(!siz) break;
		for(int i = 0;i < siz;i++){
			P p = que.front();que.pop();
			for(int j = 0;j < 6;j++){
				int nx = p.first + dx[j],ny = p.second + dy[j];
				if(nx >= 1 && ny >= 1 && nx <= n && ny <= nx && d[nx][ny] == INF){
					d[nx][ny] = t + 1;
					que.push(P(nx,ny));
				}
			}
		}
	}
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= n;j++){
			a[i][j] = a[i - 1][j] + a[i][j - 1] - a[i - 1][j - 1] + d[i][j];
			b[i][j] = b[i - 1][j - 1] + a[i][j] - a[i][j - 1];
		}
	}
	for(int i = 1;i <= n;i++){
		int lst = 0;
		for(int j = i;j <= n;j++){
			while(j + lst <= n && a[lst + j][i + lst] - b[lst + j - 1][i + lst] - a[lst + j][i - 1] + (j >= 2 ? b[j - 2][i - 1] : 0) < p) lst++;
			ans += n - j - --lst;
		}
	}
	cout << ans << endl;
	return 0;
}