#include<bits/stdc++.h>
#define int long long
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
bool st;
using namespace std;
template<typename T>istream&operator>>(istream&I,vector<T>&v){for(auto&i:v)I>>i;return I;}
template<typename T>ostream&operator<<(ostream&O,vector<T> v){for(auto i:v)O<<i<<' ';return O;}
string TMP,STR;
stringstream CIN;
void read_all(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
#ifdef debug
	cerr<<"----------------------------------- START -----------------------------------\n";
	while(getline(cin,TMP))STR+=TMP,STR+='\n';
	CIN.str(STR);
	cerr<<"\n--------------------------------- INPUT END ---------------------------------\n";
#endif
}
#ifdef debug
#define cin CIN
#endif
namespace AC{
int dx[]={0,1,0,-1,1,-1};
int dy[]={1,0,-1,0,-1,1};
int N,K,x,y,l,r,qx[10000000],qy[10000000],v[4010][4010],sx[4010][4010],sy[4010][4010];int X;
void solve(){
	cin>>N>>K>>X;
	for(int i=0;i<N;i++){
		for(int j=0;j<N-i;j++){
			v[i][j]=-1;
		}
	}
	for(int i=0;i<K;i++){
		cin>>x>>y;
		x=x-y,y--;
		if(v[x][y]==-1)v[x][y]=0,qx[r]=x,qy[r++]=y;
	}
	while(l!=r){
		x=qx[l],y=qy[l++];
		for(int i=0;i<6;i++){
			int tx=x+dx[i],ty=y+dy[i];
			if(0<=tx&&tx<N&&0<=ty&&ty<N&&0<=tx+ty&&tx+ty<N&&v[tx][ty]==-1){
				v[tx][ty]=v[x][y]+1;
				qx[r]=tx,qy[r++]=ty;
			}
		}
	}
	for(int i=0;i<N;i++){
		for(int j=0;j<N-i;j++){
			sx[i][j+1]=sx[i][j]+v[i][j];
			sy[i][j+1]=sy[i][j]+v[j][i];
		}
	}
	int ret=0;
	for(int i=0;i<N;i++){
		int cx=i+1;int cs=0;
		for(int j=0;j<=i;j++){
			while(cx!=0){
				int delta=sy[cx-1][i-cx+2]-sy[cx-1][j];
				if(cs+delta>=X)break;
				cs+=delta;
				cx--;
			}
			ret+=cx;
			cs-=sx[j][i-j+1]-sx[j][cx];
		}
	}
	cout<<ret;
}
}
bool ed;
signed main(){
	chrono::steady_clock::time_point St=chrono::steady_clock::now();
	read_all();
	chrono::steady_clock::time_point ST=chrono::steady_clock::now();
	int t=1;
	//cin>>t;
	while(t--)AC::solve();
	chrono::steady_clock::time_point ED=chrono::steady_clock::now();
	cerr<<setprecision(3)<<fixed<<"\n\n------------------------------------ END ------------------------------------\n"<<"Total Time   : "<<left<<setw(10)<<chrono::duration_cast<chrono::milliseconds>(ED-St).count()<<" \tms\n"<<"Real  Time   : "<<left<<setw(10)<<chrono::duration_cast<chrono::milliseconds>(ED-ST).count()<<" \tms\n"<<"             : "<<left<<setw(10)<<chrono::duration_cast<chrono::microseconds>(ED-ST).count()<<" \t?s\n\n"<<"Total Memory : "<<left<<setw(10)<<(&ed-&st)/1048576.0<<" \tMB\n"<<"               "<<left<<setw(10)<<(&ed-&st)/1024.0<<" \tKB\n"<<"               "<<left<<setw(10)<<(&ed-&st)<<" \tByte\n";
}