#include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<string>
#include<chrono>
#include<functional>
#include<iterator>
#include<random>
#include<unordered_set>
#include<unordered_map>
#include<array>
#include<map>
#include<bitset>
#include<iomanip>
#include<list>
#include <numeric>
using namespace std;
typedef unsigned long long int ulint;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
#define RE return 0
//ios::sync_with_stdio(false);
//std::cin.tie(0);
//<< setprecision(20)
const int mod=(int)1e9+7;
const llint big=(llint)44e15;
const long double pai=3.141592653589793238462643383279502884197;
const long double ena=2.71828182845904523536;
const long double eps=1e-7;
template <class T,class U>void mineq(T& a,U b){if(a>b){a=b;}}
template <class T,class U>void maxeq(T& a,U b){if(a<b){a=b;}}
template <class T> void soun(T& ar)
{sort(ar.begin(),ar.end());ar.erase(unique(ar.begin(),ar.end()),ar.end());}
llint gcd(llint a,llint b){if(a%b==0){return b;}else{return gcd(b,a%b);}}
llint lcm(llint a,llint b){return a/gcd(a,b) *b;}
template<class T,class U> auto LB(T& ve,U in){return lower_bound(ve.begin(),ve.end(),in);}
template<class T,class U> auto UB(T& ve,U in){return upper_bound(ve.begin(),ve.end(),in);}
template<class T,class U> auto LBI(T& ve,U in){return LB(ve,in)-ve.begin();}
template<class T,class U> auto UBI(T& ve,U in){return UB(ve,in)-ve.begin();}
template<class T> void SO(T& ve){sort(ve.begin(),ve.end());}
template<class T> void REV(T& ve){reverse(ve.begin(),ve.end());}
int main(void){
	//ういーんビートビートひるどww
	llint n,K,p,i,j;cin>>n>>K>>p;
	static int a[4002][4002];
	for(i=1;i<=n;i++){
		for(j=1;j<=i;j++){a[i][j]=mod;}
	}
	for(i=0;i<K;i++){int x,y;cin>>x>>y;a[x][y]=0;}
	for(i=1;i<=n;i++){
		for(j=1;j<i;j++){mineq(a[i][j+1],a[i][j]+1);}
		for(j=i;j>1;j--){mineq(a[i][j-1],a[i][j]+1);}
	}
	for(i=1;i<n;i++){
		for(j=1;j<=i;j++){mineq(a[i+1][j+1],a[i][j]+1);}
		for(j=1;j<=i;j++){mineq(a[i+1][j],a[i][j]+1);}
	}
	for(i=n;i>1;i--){
		for(j=1;j<i;j++){mineq(a[i-1][j],a[i][j]+1);}
		for(j=2;j<=i;j++){mineq(a[i-1][j-1],a[i][j]+1);}
	}
	//aの値が求まった
	static llint wata[4002][4002]={0};//縦累積和
	static llint wana[4002][4002]={0};//ななめ累積和
	static llint wayo[4002][4002]={0};//ななめ累積和
	for(i=1;i<=n;i++){for(j=1;j<=i;j++){
		wata[i][j]=a[i][j]+wata[i-1][j];
		wana[i][j]=a[i][j]+wana[i-1][j-1];
		wayo[i][j]=a[i][j]+wayo[i][j-1];
	}}
	llint ans=0;
	array<llint,4002> gen={0};//現在の三角の数字
	array<int,4002> made={0};//どこまで
	for(i=1;i<=n;i++){
		array<llint,4002>ngen;
		array<int,4002>nmade;
		for(j=1;j<=i;j++){
			int dco=max(made[j-1],made[j]);
			llint now=0;
			if(dco==made[j-1]){now=gen[j-1]-wata[dco][j-1]+wata[i-1][j-1]-a[i-1][j-1];}
			else{now=gen[j]-wana[dco][dco-i+j+1]+wana[i-1][j]-a[i-1][j];}
			//cerr<<wata[i][j]<<" ";
			while(dco<=n&&now<p){
				dco++;
				now+=wayo[dco][dco-i+j]-wayo[dco][j-1];
			}
			
			ans+=1+n-dco;
			ngen[j]=now;
			nmade[j]=dco;
			
		}
		//cerr<<endl;
		swap(gen,ngen);
		swap(made,nmade);
	}
	cout<<ans<<endl;
}