#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=4010;
const int INF=0x3f3f3f3f3f3f3f3f;
const int dx[]={-1,-1,0,0,1,1};
const int dy[]={-1,0,-1,1,0,1};
int n,k,p;
int ans;
int x[N],y[N];
int a[N][N];
int s[N][N];
int ss[N][N];
void bfs(){
	queue<pair<int,int> >q;
	memset(a,0x3f,sizeof(a));
	for(int i=1;i<=k;i++){
		q.push(make_pair(x[i],y[i]));
		a[x[i]][y[i]]=0;
	}
	while(!q.empty()){
		int x=q.front().first;
		int y=q.front().second;
		q.pop();
		for(int i=0;i<6;i++){
			int nx=x+dx[i];
			int ny=y+dy[i];
			if(nx<1||nx>n||ny<1||ny>nx)continue;
			if(a[nx][ny]!=INF)continue;
			q.push(make_pair(nx,ny));
			a[nx][ny]=a[x][y]+1;
		}
	}
	return;
}
int rec_cal(int x,int y,int x2,int y2){
	return ss[x2][y2]-ss[x-1][y2]-ss[x2][y-1]-ss[x-1][y-1];
}
int cal(int x,int y,int h){
	int xx=x+h-1;
	int yy=y+h-1;
	int sum=0;
	sum+=s[xx][yy];
	sum-=s[x-1][y-1];
	sum-=rec_cal(x,1,xx,y-1);
	return sum;
}
signed main(){
	// ios::sync_with_stdio(0);
	// cin.tie(0);
	// cout.tie(0);
	// freopen("triangle.in","r",stdin);
	// freopen("triangle.out","w",stdout);
	cin>>n>>k>>p;
	for(int i=1;i<=k;i++)cin>>x[i]>>y[i];
	bfs();
	// for(int i=1;i<=n;i++,cerr<<"\n")
	// 	for(int j=1;j<=i;j++)
	// 		cerr<<a[i][j]<<" ";
	for(int i=1;i<=n;i++){
		for(int j=1;j<=i;j++){
			ss[i][j]=a[i][j]+ss[i-1][j]+ss[i][j-1]-ss[i-1][j-1];
		}
	}
	for(int i=1;i<=n;i++){
		s[i][1]=a[i][1];
		for(int j=2;j<=i;j++){
			s[i][j]=s[i-1][j-1]+rec_cal(i,1,i,j);
		}
	}
	// cerr<<cal(3,1,1)<<"\n";
	for(int i=1;i<=n;i++){
		for(int j=1;j<=i;j++){
			int l=1,r=n-i+1,mid;
			int res=n-i+2;
			while(l<=r){
				mid=(l+r)>>1;
				if(cal(i,j,mid)>=p){
					res=mid;
					r=mid-1;
				}
				else l=mid+1;
			}
			// cerr<<i<<" "<<j<<" "<<n-i-res+2<<"\n";
			ans+=n-i-res+2;
		}
	}
	cout<<ans<<"\n";
	return 0;
}
/*

*/